chore: regens API reference docs (#889)

diff --git a/docs/dyn/gmail_v1.users.messages.attachments.html b/docs/dyn/gmail_v1.users.messages.attachments.html
index a5ea7fb..5b80915 100644
--- a/docs/dyn/gmail_v1.users.messages.attachments.html
+++ b/docs/dyn/gmail_v1.users.messages.attachments.html
@@ -75,24 +75,36 @@
 <h1><a href="gmail_v1.html">Gmail API</a> . <a href="gmail_v1.users.html">users</a> . <a href="gmail_v1.users.messages.html">messages</a> . <a href="gmail_v1.users.messages.attachments.html">attachments</a></h1>
 <h2>Instance Methods</h2>
 <p class="toc_element">
-  <code><a href="#get">get(userId, messageId, id)</a></code></p>
+  <code><a href="#get">get(userId, messageId, id, x__xgafv=None)</a></code></p>
 <p class="firstline">Gets the specified message attachment.</p>
 <h3>Method Details</h3>
 <div class="method">
-    <code class="details" id="get">get(userId, messageId, id)</code>
+    <code class="details" id="get">get(userId, messageId, id, x__xgafv=None)</code>
   <pre>Gets the specified message attachment.
 
 Args:
-  userId: string, The user's email address. The special value me can be used to indicate the authenticated user. (required)
+  userId: string, The user's email address. The special value &lt;code&gt;me&lt;/code&gt;
+can be used to indicate the authenticated user. (required)
   messageId: string, The ID of the message containing the attachment. (required)
   id: string, The ID of the attachment. (required)
+  x__xgafv: string, V1 error format.
+    Allowed values
+      1 - v1 error format
+      2 - v2 error format
 
 Returns:
   An object of the form:
 
     { # The body of a single MIME message part.
-    "data": "A String", # The body data of a MIME message part as a base64url encoded string. May be empty for MIME container types that have no message body or when the body data is sent as a separate attachment. An attachment ID is present if the body data is contained in a separate attachment.
-    "attachmentId": "A String", # When present, contains the ID of an external attachment that can be retrieved in a separate messages.attachments.get request. When not present, the entire content of the message part body is contained in the data field.
+    "data": "A String", # The body data of a MIME message part as a base64url encoded string.
+        # May be empty for MIME container
+        # types that have no message body or when the body data is sent as a
+        # separate attachment. An attachment ID is present if the body data is
+        # contained in a separate attachment.
+    "attachmentId": "A String", # When present, contains the ID of an external attachment that can be
+        # retrieved in a separate &lt;code&gt;messages.attachments.get&lt;/code&gt; request.
+        # When not present, the entire content of the message part body is
+        # contained in the data field.
     "size": 42, # Number of bytes for the message part data (encoding notwithstanding).
   }</pre>
 </div>