Summary:
Ran this:
```
./gradlew wrapper --gradle-version=5.6.4 --distribution-type=bin
```
I tried to get us to 6.1, but that causes some type errors within
the Android plugin. I hope it's actually there stuff and not ours
so we can upgrade once they've sorted their stuff.
Pull Request resolved: https://github.com/facebook/flipper/pull/749
Test Plan:
./gradlew tasks
./gradlew :sample:installDebug
Reviewed By: jknoxville
Differential Revision: D19428496
Pulled By: passy
fbshipit-source-id: a910f5a269688f7ec5fc020fe1af99a75fc7b574
e84f62d5d5