Fix RTMP library gradle file.

(GitHub issue #3038)

Module prefix was missing for library-core module.

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=161366375

extensions/rtmp/build.gradle

@@ -27,6 +27,6 @@ android {
 }
 }
 
 
 dependencies {
 dependencies {
-    compile project(':library-core')
+    compile project(modulePrefix + 'library-core')
     compile 'net.butterflytv.utils:rtmp-client:0.2.7.1'
     compile 'net.butterflytv.utils:rtmp-client:0.2.7.1'
 }
 }