Release v1.6.0 (#324)

* Update version and changelog for v1.6.0
* Update docs
diff --git a/docs/dyn/groupsmigration_v1.archive.html b/docs/dyn/groupsmigration_v1.archive.html
index 8bf8875..87035c0 100644
--- a/docs/dyn/groupsmigration_v1.archive.html
+++ b/docs/dyn/groupsmigration_v1.archive.html
@@ -75,16 +75,17 @@
 <h1><a href="groupsmigration_v1.html">Groups Migration API</a> . <a href="groupsmigration_v1.archive.html">archive</a></h1>
 <h2>Instance Methods</h2>
 <p class="toc_element">
-  <code><a href="#insert">insert(groupId, media_body=None)</a></code></p>
+  <code><a href="#insert">insert(groupId, media_body=None, media_mime_type=None)</a></code></p>
 <p class="firstline">Inserts a new mail into the archive of the Google group.</p>
 <h3>Method Details</h3>
 <div class="method">
-    <code class="details" id="insert">insert(groupId, media_body=None)</code>
+    <code class="details" id="insert">insert(groupId, media_body=None, media_mime_type=None)</code>
   <pre>Inserts a new mail into the archive of the Google group.
 
 Args:
   groupId: string, The group ID (required)
   media_body: string, The filename of the media request body, or an instance of a MediaUpload object.
+  media_mime_type: string, The MIME type of the media request body, or an instance of a MediaUpload object.
 
 Returns:
   An object of the form: