Fix persistent-volumes url (#1309)

stable/chronograf/README.md

@@ -68,4 +68,4 @@ $ helm install --name my-release -f values.yaml stable/chronograf
 
 The [Chronograf](https://quay.io/influxdb/chronograf) image stores data in the `/var/lib/chronograf` directory in the container.
 
-The chart optionally mounts a [Persistent Volume](kubernetes.io/docs/user-guide/persistent-volumes/) volume at this location. The volume is created using dynamic volume provisioning.
+The chart optionally mounts a [Persistent Volume](http://kubernetes.io/docs/user-guide/persistent-volumes/) volume at this location. The volume is created using dynamic volume provisioning.

stable/influxdb/README.md

@@ -69,7 +69,7 @@ $ helm install --name my-release -f values.yaml stable/influxdb
 
 The [InfluxDB](https://hub.docker.com/_/influxdb/) image stores data in the `/var/lib/influxdb` directory in the container.
 
-The chart mounts a [Persistent Volume](kubernetes.io/docs/user-guide/persistent-volumes/) volume at this location. The volume is created using dynamic volume provisioning.
+The chart mounts a [Persistent Volume](http://kubernetes.io/docs/user-guide/persistent-volumes/) volume at this location. The volume is created using dynamic volume provisioning.
 
 ## Starting with authentication
 

stable/kapacitor/README.md

@@ -88,4 +88,4 @@ $ helm install --name my-release -f values.yaml stable/kapacitor
 
 The [Kapacitor](https://hub.docker.com/_/kapacitor/) image stores data in the `/var/lib/kapacitor` directory in the container.
 
-The chart optionally mounts a [Persistent Volume](kubernetes.io/docs/user-guide/persistent-volumes/) volume at this location. The volume is created using dynamic volume provisioning.
\ No newline at end of file
+The chart optionally mounts a [Persistent Volume](http://kubernetes.io/docs/user-guide/persistent-volumes/) volume at this location. The volume is created using dynamic volume provisioning.
\ No newline at end of file