Update installation.md

Changed Todo for "Todo" on line 71, because if created without quotes a problem arises later, while trying to enable the Android platform. As mentioned here: http://stackoverflow.com/questions/18193077/phonegap-3-0-phonegap-platform-build-android-returns-success-but-buildfile-do
Merge pull request #130 from andresgottlieb/patch-1

Update installation.md