fix: yaml parsing build_image_version default as double

Author: devnev

src/jobs/android_build.yml

@@ -58,7 +58,7 @@ parameters:
   build_image_version:
     description: React Native Android build image version. For available veresions, see https://hub.docker.com/r/reactnativecommunity/react-native-android/tags
     type: string
-    default: 5.1
+    default: '5.1'
   resource_class:
     description: Changes the resource class of the executor. Requires a support request to enable the resource_class parameter. See https://circleci.com/docs/2.0/configuration-reference/#resource_class
     type: string