capybara needs qt5 to work with react. OSX probably has qt 4 installed by default.
thoughtbot/capybara-webkit#666
brew uninstall qt
brew install qt5
brew linkapps qt5
brew doctor
gem uninstall capybara-webkit
# use correct path to qt5 version:
# https://github.com/thoughtbot/capybara-webkit/issues/678
QMAKE=/usr/local/Cellar/qt5/5.4.2/bin/qmake bundle install
brew uninstall qt
brew tap homebrew/versions
brew install qt55
brew linkapps qt55
brew doctor
gem uninstall capybara-webkit
QMAKE=/usr/local/Cellar/[email protected]/5.5.1/bin/qmake bundle install