Android : getString should be extras.getString

Plugin was failing to build : 

[javac] Compiling 8 source files to (...)/platforms/android/bin/classes
[javac] (...)/platforms/android/src/com/plugin/gcm/GCMIntentService.java:96: cannot find symbol
[javac] symbol  : method getString(java.lang.String)
[javac] location: class com.plugin.gcm.GCMIntentService
[javac]                 .setTicker(getString("title"))