Update .gitignore to new dart_tool pub cache

bcko · Sebastian Kocks · commit 3ae0cbc6e5bd · 2018-06-05T22:42:08.000+02:00
dart-lang/sdk#32030
diff --git a/.gitignore b/.gitignore
@@ -2,6 +2,7 @@
 .atom/
 .idea
 .packages
+.dart_tool/
 .pub/
 build/
 ios/.generated/
