Update changelog for 0.2.1 release (#51)

Author: gotjosh

CHANGELOG.md

@@ -2,10 +2,12 @@
 
 ## unreleased / master
 
+## v0.2.1 / 2020-06-08
+
 * [FEATURE] Add `rules check` command. It runs various [best practice](https://prometheus.io/docs/practices/rules/) checks against rules.
 * [ENHANCEMENT] Ensure `rules prepare` takes into account Vector Matching on PromQL Binary Expressions.
 
-## v0.2.0 / 2020-03-10
+## v0.2.0 / 2020-06-02
 
 * [FEATURE] Add `rules prepare` command. It allows you add a label to PromQL aggregations and lint your expressions in rule files.
 * [FEATURE] Add `rules lint` command. It lints, rules YAML and PromQL expression formatting within the rule file