Add .flutter-plugins-dependencies to .gitignore

[AliAbdelfattah]

Summary of Changes

Adds .flutter-plugins-dependencies to .gitignore

Checklist

• In addition to adding the new API to Dart, I have also added its implementation to both iOS and Android.
• I have added at least 1 unit test in Dart for the new API and made sure the tests pass locally.
• I have updated README.md to add the new API.

[codecov]

Codecov Report

Merging #146 (e20f75e) into master (f9e030a) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #146   +/-   ##
=======================================
  Coverage   73.15%   73.15%           
=======================================
  Files          14       14           
  Lines         555      555           
=======================================
  Hits          406      406           
  Misses        149      149           

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