Update version strings

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=176989632

README.md

@@ -42,18 +42,18 @@ Next add a gradle compile dependency to the `build.gradle` file of your app
 module. The following will add a dependency to the full library:
 
 ```gradle
-compile 'com.google.android.exoplayer:exoplayer:r2.X.X'
+compile 'com.google.android.exoplayer:exoplayer:2.X.X'
 ```
 
-where `r2.X.X` is your preferred version. Alternatively, you can depend on only
+where `2.X.X` is your preferred version. Alternatively, you can depend on only
 the library modules that you actually need. For example the following will add
 dependencies on the Core, DASH and UI library modules, as might be required for
 an app that plays DASH content:
 
 ```gradle
-compile 'com.google.android.exoplayer:exoplayer-core:r2.X.X'
-compile 'com.google.android.exoplayer:exoplayer-dash:r2.X.X'
-compile 'com.google.android.exoplayer:exoplayer-ui:r2.X.X'
+compile 'com.google.android.exoplayer:exoplayer-core:2.X.X'
+compile 'com.google.android.exoplayer:exoplayer-dash:2.X.X'
+compile 'com.google.android.exoplayer:exoplayer-ui:2.X.X'
 ```
 
 The available library modules are listed below. Adding a dependency to the full