update gradle to 6.1.1
somewhat arbitrary version selection, but this matches what's currently
in use in ExoPlayer in the dev-v2 branch
fixes:
FAILURE: Build failed with an exception.
* What went wrong:
Could not determine java version from '11.0.9.1'.
and removes the wrapper task as this is predefined in later versions:
Build file '/home/jzern/external/libwebp/build.gradle' line: 437
* What went wrong:
A problem occurred evaluating root project 'libwebp'.
> Cannot add task 'wrapper' as a task with that name already exists.
Change-Id: Ib9ef757d874cd6d4b08da3e7cef3ac5316935966
6 files changed
