changelog: /s/backward compatible/forward compatible/ (#4600)

Fixes #4597

Signed-off-by: Goutham Veeramachaneni <gouthamve@gmail.com>

CHANGELOG.md

@@ -1,13 +1,13 @@
 ## 2.4.0 / 2018-09-11
 
-This release includes multiple bugfixes and features. Further, the WAL implementation has been re-written so the storage is not backward compatible. Prometheus 2.3 storage will work on 2.4 but not vice-versa.
+This release includes multiple bugfixes and features. Further, the WAL implementation has been re-written so the storage is not forward compatible. Prometheus 2.3 storage will work on 2.4 but not vice-versa.
 
 * [CHANGE] Reduce remote write default retries #4279
 * [CHANGE] Remove /heap endpoint #4460
 * [FEATURE] Persist alert 'for' state across restarts #4061
 * [FEATURE] Add API providing per target metric metadata #4183
 * [FEATURE] Add API providing recording and alerting rules #4318 #4501
-* [ENHANCEMENT] Brand new WAL implementation for TSDB. Backwards incompatible with previous WAL. 
+* [ENHANCEMENT] Brand new WAL implementation for TSDB. Forwards incompatible with previous WAL. 
 * [ENHANCEMENT] Show rule evaluation errors in UI #4457 
 * [ENHANCEMENT] Throttle resends of alerts to Alertmanager #4538
 * [ENHANCEMENT] Send EndsAt along with the alert to Alertmanager #4550