add myself as owner of prometheus chart (#5195)

* add myself as an owner of prometheus chart

* Update Chart.yaml

stable/prometheus/Chart.yaml

@@ -1,5 +1,5 @@
 name: prometheus
-version: 6.3.0
+version: 6.3.1
 appVersion: 2.2.1
 description: Prometheus is a monitoring system and time series database.
 home: https://prometheus.io/
@@ -13,4 +13,6 @@ sources:
 maintainers:
   - name: mgoodness
     email: mgoodness@gmail.com
+  - name: gianrubio
+    email: gianrubio@gmail.com
 engine: gotpl

stable/prometheus/OWNERS

@@ -1,4 +1,6 @@
 approvers:
 - mgoodness
+- gianrubio
 reviewers:
 - mgoodness
+- gianrubio