stackdriver: revert an accidental commit for text template variable

with dummy change in readme to be able to make a commit

public/app/plugins/datasource/stackdriver/README.md

-# Stackdriver Datasource -  Native Plugin
+# Stackdriver Datasource - Native Plugin
 
 Grafana ships with built-in support for Google Stackdriver. You just have to add it as a datasource and you will be ready to build dashboards for your Stackdriver metrics.