Fix description of MySQL alert

Author: priteau

etc/kayobe/kolla/config/prometheus/mysql.rules

@@ -58,7 +58,7 @@ groups:
       severity: warning
     annotations:
       summary: "MySQL Slave replication lag (instance {{ $labels.instance }})"
-      description: "MysqL replication lag on {{ $labels.instance }}"
+      description: "MySQL replication lag on {{ $labels.instance }}"
 
   - alert: MysqlSlowQueries
     expr: increase(mysql_global_status_slow_queries[1m]) > 0