update changelog / upgrade warning to be clearer about backward compatibility

CHANGES.md

@@ -2,6 +2,7 @@
 
 | DateOfChange   | Changes                                                                                                      |
 |----------------|--------------------------------------------------------------------------------------------------------------|
+| Jul 10, 2017   | Update Google API Client. May break backwards compatibility for GoogleCalendarPublishAgent. [2047](https://github.com/huginn/huginn/pull/2047)   |
 | Oct 17, 2016   | Normalize URL in `to_uri` and `uri_expand` liquid filters.                                                   |
 | Oct 06, 2016   | `RssAgent` is reimplemented migrating its underlying feed parser from FeedNormalizer to Feedjira. [1564](https://github.com/cantino/huginn/pull/1564)     |
 | Oct 05, 2016   | Migrate to Rails 5. [1688](https://github.com/cantino/huginn/pull/1688)                                      |

app/views/application/_upgrade_warning.html.erb

@@ -31,6 +31,8 @@ TWITTER_OAUTH_SECRET=<%= @twitter_oauth_secret %>
         <b>Warning!</b> Your <b>Google Calendar Publish Agents</b> are using an outdated version of Google Auth. You need to update the agent configuration, possibly with a new keyfile from Google for it to continue to work.
       <br/>
         PKCS12 key files (`.p12`) are no longer supported. Instead use RSA private keys. Edit the agents to see the updated instructions. The `google.key_secret` option is no longer needed, please remove it.
+      <br/>
+        The format of parameters in events passed to the agent have also changed. Parameters now are expected in underscore_case instead of camelCase (to match Ruby convention). Please update upstream agents that send events to the calendar agent.
       </p>
       <p>
         Outdated agents: