Update minSdkVersion to match ActionBarSherlock

Since the project requires ActionBarSherlock, the minSdkVersion shouldn't be less than the minSdkVersion of ActionBarSherlock.

Probably not completely necessary but it was causing my gradle build to complain about version numbers when it tried to merge the manifests.
Merge pull request #9 from intrications/master

Update minSdkVersion to match ActionBarSherlock