Rename gitignore to .gitignore

Author: RenugaSadagoban98

gitignore renamed to .gitignore

@@ -75,4 +75,4 @@ svc-keyfile.json
 !**/ios/**/default.mode2v3
 !**/ios/**/default.pbxuser
 !**/ios/**/default.perspectivev3
-!/packages/flutter_tools/test/data/dart_dependencies_test/**/.packages
+!/packages/flutter_tools/test/data/dart_dependencies_test/**/.packages