Add a space delimiter to duplicated hash keys

spec/ameba/rule/hash_duplicated_key_spec.cr

@@ -44,7 +44,7 @@ module Ameba::Rule
       )
       subject.catch(s).should_not be_valid
       error = s.errors.first
-      error.message.should eq %(Duplicated keys in hash literal: "key1","key2")
+      error.message.should eq %(Duplicated keys in hash literal: "key1", "key2")
     end
   end
 end

src/ameba/rule/hash_duplicated_key.cr

@@ -33,7 +33,7 @@ module Ameba::Rule
       return unless (keys = duplicated_keys(node.entries)).any?
 
       source.error self, node.location,
-        "Duplicated keys in hash literal: #{keys.join(",")}"
+        "Duplicated keys in hash literal: #{keys.join(", ")}"
     end
 
     private def duplicated_keys(entries)