Summary:
Update the LeakCanary 2 plugin version in LeakCanary 2 plugin doc
While adding the version as in the doc, the import statements didn't work. Upon checking the maven repo, I found out that the latest version is `0.81.0`. Updating to the latest version helps
## Changelog
Updated LeakCanary 2 plugin docs to include the latest plugin version
Pull Request resolved: https://github.com/facebook/flipper/pull/2085
Test Plan: Not necessary
Reviewed By: mweststrate
Differential Revision: D27265598
Pulled By: passy
fbshipit-source-id: 2f82689c1f075c2f9cff8bae2831c9780a3db697
0bf786544a