Use the 0.x.x gem for webpacker 3.x.x

Author: ytbryan

vue

@@ -1,5 +1,5 @@
-gem 'webpacker'
-gem 'vueonrails', github: "vueonrails/vueonrails"
+gem 'webpacker', '~> 3.x.x'
+gem 'vueonrails', '~> 0.x.x'
 route "mount Vueonrails::Engine, at: 'vue'"
 
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