Podfile

source 'https://github.com/CocoaPods/Specs.git'
platform :ios, '9.0'

target 'YOUR_PROJECT_NAME' do
  pod 'ExpoKit',
    :git => "http://github.com/expo/expo.git",
    :tag => "ios/2.7.0",
    :subspecs => [
      "Core"
    ],
    :inhibit_warnings => true
  pod 'EXGL',
    :path => "../node_modules/expo/node_modules/expo-gl/ios",
    :inhibit_warnings => true
  pod 'EXCore',
    :path => "../node_modules/expo/node_modules/expo-core/ios",
    :inhibit_warnings => true
  pod 'EXCamera',
    :path => "../node_modules/expo/node_modules/expo-camera/ios",
    :inhibit_warnings => true
  pod 'EXSensors',
    :path => "../node_modules/expo/node_modules/expo-sensors/ios",
    :inhibit_warnings => true
  pod 'EXConstants',
    :path => "../node_modules/expo/node_modules/expo-constants/ios",
    :inhibit_warnings => true
  pod 'EXFileSystem',
    :path => "../node_modules/expo/node_modules/expo-file-system/ios",
    :inhibit_warnings => true
  pod 'EXPermissions',
    :path => "../node_modules/expo/node_modules/expo-permissions/ios",
    :inhibit_warnings => true
  pod 'EXCameraInterface',
    :path => "../node_modules/expo/node_modules/expo-camera-interface/ios",
    :inhibit_warnings => true
  pod 'EXSensorsInterface',
    :path => "../node_modules/expo/node_modules/expo-sensors-interface/ios",
    :inhibit_warnings => true
  pod 'EXConstantsInterface',
    :path => "../node_modules/expo/node_modules/expo-constants-interface/ios",
    :inhibit_warnings => true
  pod 'EXReactNativeAdapter',
    :path => "../node_modules/expo/node_modules/expo-react-native-adapter/ios",
    :inhibit_warnings => true
  pod 'EXFileSystemInterface',
    :path => "../node_modules/expo/node_modules/expo-file-system-interface/ios",
    :inhibit_warnings => true
  pod 'EXPermissionsInterface',
    :path => "../node_modules/expo/node_modules/expo-permissions-interface/ios",
    :inhibit_warnings => true
  pod 'EXFaceDetectorInterface',
    :path => "../node_modules/expo/node_modules/expo-face-detector-interface/ios",
    :inhibit_warnings => true
  pod 'EXSMS',
    :path => "../node_modules/expo/node_modules/expo-sms/ios",
    :inhibit_warnings => true
  pod 'EXGL-CPP',
    :path => "../node_modules/expo/node_modules/expo-gl-cpp/cpp",
    :inhibit_warnings => true

  pod 'React',
    :path => "../node_modules/react-native",
    :inhibit_warnings => true,
    :subspecs => [
      "Core",
      "ART",
      "RCTActionSheet",
      "RCTAnimation",
      "RCTCameraRoll",
      "RCTGeolocation",
      "RCTImage",
      "RCTNetwork",
      "RCTText",
      "RCTVibration",
      "RCTWebSocket",
      "DevSupport",
      "CxxBridge"
    ]
  pod 'yoga',
    :path => "../node_modules/react-native/ReactCommon/yoga",
    :inhibit_warnings => true
  pod 'DoubleConversion',
    :podspec => "../node_modules/react-native/third-party-podspecs/DoubleConversion.podspec",
    :inhibit_warnings => true
  pod 'Folly',
    :podspec => "../node_modules/react-native/third-party-podspecs/Folly.podspec",
    :inhibit_warnings => true
  pod 'glog',
    :podspec => "../node_modules/react-native/third-party-podspecs/glog.podspec",
    :inhibit_warnings => true


  post_install do |installer|
    installer.pods_project.main_group.tab_width = '2';
    installer.pods_project.main_group.indent_width = '2';

    installer.pod_targets.each do |target|

    if target.pod_name == 'ExpoKit'
      target.native_target.build_configurations.each do |config|
        config.build_settings['GCC_PREPROCESSOR_DEFINITIONS'] ||= ['$(inherited)']
        config.build_settings['GCC_PREPROCESSOR_DEFINITIONS'] << 'EX_DETACHED=1'
        
        # needed for GoogleMaps 2.x
        config.build_settings['FRAMEWORK_SEARCH_PATHS'] ||= []
        config.build_settings['FRAMEWORK_SEARCH_PATHS'] << '${PODS_ROOT}/GoogleMaps/Base/Frameworks'
        config.build_settings['FRAMEWORK_SEARCH_PATHS'] << '${PODS_ROOT}/GoogleMaps/Maps/Frameworks'
      end
    end


    if ['Amplitude-iOS','Analytics','AppAuth','Branch','CocoaLumberjack','FBSDKCoreKit','FBSDKLoginKit','FBSDKShareKit','GPUImage','JKBigInteger2'].include? target.pod_name
      target.native_target.build_configurations.each do |config|
        config.build_settings['IPHONEOS_DEPLOYMENT_TARGET'] = '9.0'
      end
    end
    # Can't specify this in the React podspec because we need
    # to use those podspecs for detached projects which don't reference ExponentCPP.
    if target.pod_name.start_with?('React')
      target.native_target.build_configurations.each do |config|
        config.build_settings['IPHONEOS_DEPLOYMENT_TARGET'] = '9.0'
        config.build_settings['HEADER_SEARCH_PATHS'] ||= ['$(inherited)']
      end
    end
    # Build React Native with RCT_DEV enabled
    next unless target.pod_name == 'React'
    target.native_target.build_configurations.each do |config|
      config.build_settings['GCC_PREPROCESSOR_DEFINITIONS'] ||= ['$(inherited)']
      config.build_settings['GCC_PREPROCESSOR_DEFINITIONS'] << 'RCT_DEV=1'
    end

    end
  end
end

I also had to add

  pod 'EXFaceDetector',
    :path => "../node_modules/expo-face-detector/ios",
    :inhibit_warnings => true

otherwise on startup I'd get errors. This is on a project which was ejected from 27 originally.