exercism#37 - memoize body_line_numbers method

Author: Hunk13

Diff for: lib/extract_test_metadata.rb

@@ -93,6 +93,7 @@ def code_for_line(one_indexed_idx)
       filelines[one_indexed_idx - 1]
     end
 
+    memoize
     def body_line_numbers
       # Get the lines excluding the first (def) and last (end)
       ((test_node.first_line + 1)..(test_node.last_line - 1))