allow more that one generatedSourceDir
allow more that one generatedSourceDir

e.g., generatedSourceDir "build/source/apt", 'build/source/base'
maxbritto/j2objc-gradle,madvay/j2objc-gradle,j2objc-contrib/j2objc-gradle,j2objc-contrib/j2objc-gradle,brunobowden/j2objc-gradle,madvay/j2objc-gradle,brunobowden/j2objc-gradle,nirmaljuthani/j2objc-gradle,madvay/j2objc-gradle,j2objc-contrib/j2objc-gradle,brunobowden/j2objc-gradle,maxbritto/j2objc-gradle,nirmaljuthani/j2objc-gradle,maxbritto/j2objc-gradle,confile/j2objc-gradle,confile/j2objc-gradle,j2objc-contrib/j2objc-gradle,brunobowden/j2objc-gradle,madvay/j2objc-gradle,maxbritto/j2objc-gradle