Enable Style/ExplicitBlockArgument cop

The code is disabled by default because in some cases
it could change the block arity which might fail if the block is
actualy a lambda.

However I enabled it on Rails and shopify-core and it went just fine.

Since this cop is beneficial for production performance and
for triming CI backtraces a bit, I think we should enable it.

rubocop.yml

@@ -468,7 +468,7 @@ Style/ExpandPathArguments:
   Enabled: false
 
 Style/ExplicitBlockArgument:
-  Enabled: false
+  Enabled: true
 
 Style/ExponentialNotation:
   Enabled: false