Fix timezone in submitted data

SimpleDateFormat uses the system's default time zone by default.
Update Android gradle plugin to 0.6.+

Android Studio 0.3.0 requires Android gradle plugin >= 0.6.0
Merge pull request #227 from illarionov/updateAndroidGradle

Update Android gradle plugin to 0.6.+
Merge pull request #226 from illarionov/fixTimeZone

Fix timezone in submitted data