update changelog

CHANGELOG.md

-### 1.2a
-- Add tests (#7)
-- Fix crash on creating a client instance with no options
+### 2.0
+- Bump node engine to node >= 6.0.x
 - Fix challonge.createClient massageProperties is tautologically true (#2)
+- Fix issues caused by previously published versions switching to request (#3)
+- Add tests at 100% coverage (#7)
+- Fix Client generating duplicate qs props created for nested objects (#13)
+- Moved helper methods into utilities (#14)
 - Fix malformed urls if an organization has a dash in the name (#15)
+- Merged changes from challonge-js fork, to be deprecated (#19)
+- Update to es6 standard let/const (#20)
+- Add jsformat and jshint for style consistancy (#22)
+- Fix crash on creating a client instance with no options
 
 ### 1.0
 - Initial Release