Merge pull request #593 from affinity/moberegger/optimize_key_method

Optimize `_key` to prevent string allocation when formatting `Symbol`s

Author: rafaelfranca

lib/jbuilder.rb

@@ -313,7 +313,13 @@ def _merge_values(current_value, updates)
   end
 
   def _key(key)
-    @key_formatter ? @key_formatter.format(key) : key.to_s
+    if @key_formatter
+      @key_formatter.format(key)
+    elsif key.is_a?(::Symbol)
+      key.name
+    else
+      key.to_s
+    end
   end
 
   def _format_keys(hash_or_array)