fix maven build failed error

### error log: 
`Failed to execute goal on project seadroid: Could not resolve dependencies for project com.seafile.seadroid2:seadroid:apk:1.0.0: Failure to find android:android:jar:4.2.2_r2 in http://repo.maven.apache.org/maven2 was cached in the local repository, resolution will not be reattempted until the update interval of central has elapsed or updates are forced`

### solution
1. choose a available android jar version according [here](http://search.maven.org/#search%7Cgav%7C1%7Cg%3a%22com.google.android%22%20AND%20a%3a%22android%22)
2. android.jar artifacts in Maven central are available with the groupId `com.google.android`. The 4.1.1.4 version was the last com.google.android:android version uploaded to Maven Central, that's why it's the latest one you can reference using com.google.android:android. [read more](http://stackoverflow.com/questions/20975751/missing-artifact-com-google-androidandroidjar4-4-r1)
3. another solution available on [stack overflow provided by S.D](http://stackoverflow.com/questions/18416295/dependencies-dependency-version-for-com-google-androidandroidjar-is-missing)