Fix file extensions and line endings (#868)

Summary:
Three related commits to fix a few file extensions/formatting. No content changes.

See discussion in #660 for some context.

cc rightparen

Pull Request resolved: #868

Reviewed By: Mxiim

Differential Revision: D25137908

Pulled By: jawwad

fbshipit-source-id: 046057e889f187ed892a939b59f085203963e7ea

README.mdown → README.md

@@ -105,7 +105,7 @@ See the [SECURITY POLICY](SECURITY.md) for more info on our bug bounty program.
 CONTRIBUTING
 -------------
 We are able to accept contributions to the Facebook SDK for Android. To contribute please do the following.
-- Follow the instructions in the [CONTRIBUTING.mdown](https://github.com/facebook/facebook-android-sdk/blob/master/CONTRIBUTING.mdown).
+- Follow the instructions in the [CONTRIBUTING.md](https://github.com/facebook/facebook-android-sdk/blob/master/CONTRIBUTING.md).
 - Submit your pull request to the [master](https://github.com/facebook/facebook-android-sdk/tree/master) branch. This allows us to merge your change into our internal master and then push out the change in the next release.
 
 LICENSE

samples/FBLoginSample/README.mdown → samples/FBLoginSample/README.md

@@ -34,7 +34,7 @@ You can also join the Facebook Developers Group on Facebook (https://www.faceboo
 Contributing
 -------------
 We are able to accept contributions to the Facebook Login Sample App for Android. To contribute please do the following.
-- Follow the instructions in the [CONTRIBUTING.mdown](https://github.com/facebook/facebook-android-sdk/tree/master/samples/FBLoginSample/CONTRIBUTING.mdown).
+- Follow the instructions in the [CONTRIBUTING.md](https://github.com/facebook/facebook-android-sdk/tree/master/samples/FBLoginSample/CONTRIBUTING.md).
 - Submit your pull request to the [dev](https://github.com/facebook/facebook-android-sdk/tree/dev) branch. This allows us to merge your change into our internal master and then push out the change in the next release.
 
 License