Enable Travis PHP Build on Windows

.travis.yml

# default os is linux

matrix:
  include:
    - language: php
      php: 7.2      
      before_script:
        - composer install
      after_script:
        - sh .travis.coverage.sh
      env:
        - COVERAGE_FLAGS="--coverage-text --coverage-clover=clover.xml"
    - name: "PHP: 7.2"
      language: sh
      os: windows
      before_script:
        # Use chocolatey to install certain php version
        # Skipp --version to install latest stable release
        - choco install php --version 7.2.15 --package-parameters='"/InstallDir:C:\php"'
        # Export windows path into unix path
        - export PATH=/c/php:$PATH
        # Enable openssl used by composer
        - sed -i 's/;extension=openssl/extension=openssl/g' /c/php/php.ini
        # Enable mbstring used by phpunit
        - sed -i 's/;extension=mbstring/extension=mbstring/g' /c/php/php.ini
        #
        # You might want to enable other extensions as needed ...
        #
        # Fetch composer 
        - wget http://getcomposer.org/composer.phar
        # Install dependencies
        - php composer.phar install

  allow_failures:
    - php: nightly

script:
  - vendor/bin/phpunit --verbose ${COVERAGE_FLAGS} --colors