Fixes wrong OSX image in travis.yml in README.md.
Fixes wrong OSX image in travis.yml in README.md.

danielaRiesgo/ios-scripts,hzalaz/ios-scripts,guidomb/ios-scripts,danielaRiesgo/ios-scripts,guidomb/ios-scripts,hzalaz/ios-scripts,danielaRiesgo/ios-scripts,guidomb/ios-scripts,guidomb/ios-scripts,hzalaz/ios-scripts