Set druid_rc_version to 0.10.1-rc2 (druid-io#406)

Author: jon-wei

_config.yml

@@ -21,7 +21,7 @@ description: 'Real²time Exploratory Analytics on Large Datasets'
 
 druid_version: 0.10.0
 
-druid_rc_version: 0.10.1-rc1
+druid_rc_version: 0.10.1-rc2
 druid_stable_version: 0.10.0
 druid_latest_version: 0.10.0