.rubocop.yml in key_tree-0.5.3 vs .rubocop.yml in key_tree-0.6.0

- old
+ new

@@ -1,4 +1,7 @@
+AllCops:
+  TargetRubyVersion: 2.3
+
 Metrics/BlockLength:
   Exclude:
     - 'spec/*_spec.rb'
 
 Style/BlockDelimiters: