Fix broken GitHubApiTest integration test

It's kinda interesting how the test was broken by this innocuous change:

pockethub@65348dd

The change is that the 'getRepositories()' method is no longer used in
the main app (replaced by 'getOrgRepositories()'), and so is stripped by
proguard, but it's still used in the integration test. With recent
changes to the android-maven-plugin, the contributing library is only
processed by proguard once, so the explicit usage in the integration
tests isn't enough to get the 'getRepositories()' method kept - an
explicit proguard rule has to be added.

proguard.cfg

@@ -66,3 +66,9 @@
 -keep class * extends com.jcraft.jsch.KeyExchange
 -keep class com.jcraft.jsch.**
 -keepclassmembers class com.github.mobile.** { public <init>(...); }
+-keep public class org.eclipse.egit.github.core.service.RepositoryService {
+ *** getRepositories(...);
+}
+-keep public class org.eclipse.egit.github.core.Repository {
+ *** getWatchers(...);
+}