CONTRIBUTING.md in polyfill-1.5.0 vs CONTRIBUTING.md in polyfill-1.6.0

- old
+ new

@@ -7,9 +7,10 @@
 
 ### Code
 
 A list of changes can be found at:
 
+ * https://raw.githubusercontent.com/ruby/ruby/v2_6_0/NEWS
  * https://raw.githubusercontent.com/ruby/ruby/v2_5_0/NEWS
  * https://raw.githubusercontent.com/ruby/ruby/v2_4_2/NEWS
  * https://raw.githubusercontent.com/ruby/ruby/v2_3_4/NEWS
  * https://raw.githubusercontent.com/ruby/ruby/v2_2_7/NEWS
 