[HOTFIX] Change the link of helium.json from S3 to zeppelin.apache.org (#4713)

Author: jongyoul

conf/zeppelin-site.xml.template

@@ -410,7 +410,7 @@
 <!--
 <property>
   <name>zeppelin.helium.registry</name>
-  <value>helium,https://s3.amazonaws.com/helium-package/helium.json</value>
+  <value>helium,https://zeppelin.apache.org/helium.json</value>
   <description>Location of external Helium Registry</description>
 </property>
 -->

docs/development/helium/overview.md

@@ -40,4 +40,4 @@ Currently, Helium supports 4 types of package.
 ## Configuration
 
 Zeppelin ships with several builtin helium plugins which is located in $ZEPPELIN_HOME/heliums. If you want to try more types of heliums plugins,
-you can configure `zeppelin.helium.registry` to be `helium,https://s3.amazonaws.com/helium-package/helium.json` in zeppelin-site.xml. `https://s3.amazonaws.com/helium-package/helium.json` will be updated regularly.
+you can configure `zeppelin.helium.registry` to be `helium,https://zeppelin.apache.org/helium.json` in zeppelin-site.xml. `https://zeppelin.apache.org/helium.json` will be updated regularly.