Fixed rocketchat_configs docs (prometheus#4217)

Signed-off-by: Reto Kupferschmid <[email protected]>
Co-authored-by: gotjosh <[email protected]>

Author: rekup

docs/configuration.md

@@ -719,7 +719,7 @@ pagerduty_configs:
   [ - <pagerduty_config>, ... ]
 pushover_configs:
   [ - <pushover_config>, ... ]
-rocket_configs:
+rocketchat_configs:
   [ - <rocketchat_config>, ... ]
 slack_configs:
   [ - <slack_config>, ... ]