Typo fixes

Issue:#3631

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=180197723

README.md

@@ -68,7 +68,7 @@ individually.
 
 In addition to library modules, ExoPlayer has multiple extension modules that
 depend on external libraries to provide additional functionality. Some
-extensions are available from JCenter, whereas others must be built manaully.
+extensions are available from JCenter, whereas others must be built manually.
 Browse the [extensions directory][] and their individual READMEs for details.
 
 More information on the library and extension modules that are available from

RELEASENOTES.md

@@ -221,7 +221,7 @@
   easy and seamless way of incorporating display ads into ExoPlayer playbacks.
   You can read more about the IMA extension
   [here](https://medium.com/google-exoplayer/playing-ads-with-exoplayer-and-ima-868dfd767ea).
-* MediaSession extension: Provides an easy to to connect ExoPlayer with
+* MediaSession extension: Provides an easy to connect ExoPlayer with
   MediaSessionCompat in the Android Support Library.
 * RTMP extension: An extension for playing streams over RTMP.
 * Build: Made it easier for application developers to depend on a local checkout