build: run docs regen in synth.py (#1059)

diff --git a/docs/dyn/chat_v1.spaces.messages.attachments.html b/docs/dyn/chat_v1.spaces.messages.attachments.html
index e053c3c..0f0e276 100644
--- a/docs/dyn/chat_v1.spaces.messages.attachments.html
+++ b/docs/dyn/chat_v1.spaces.messages.attachments.html
@@ -101,18 +101,18 @@
   An object of the form:
 
     { # An attachment in Hangouts Chat.
-    "source": "A String", # The source of the attachment.
-    "contentType": "A String", # The content type (MIME type) of the file.
-    "name": "A String", # Resource name of the attachment, in the form "spaces/*/messages/*/attachments/*".
-    "contentName": "A String", # The original file name for the content, not the full path.
     "driveDataRef": { # A reference to the data of a drive attachment. # A reference to the drive attachment. This is used with the Drive API.
       "driveFileId": "A String", # The id for the drive file, for use with the Drive API.
     },
-    "downloadUri": "A String", # Output only. The download URL which should be used to allow a human user to download the attachment. Bots should not use this URL to download attachment content.
     "attachmentDataRef": { # A reference to the data of an attachment. # A reference to the attachment data. This is used with the media API to download the attachment data.
       "resourceName": "A String", # The resource name of the attachment data. This is used with the media API to download the attachment data.
     },
+    "contentName": "A String", # The original file name for the content, not the full path.
     "thumbnailUri": "A String", # Output only. The thumbnail URL which should be used to preview the attachment to a human user. Bots should not use this URL to download attachment content.
+    "contentType": "A String", # The content type (MIME type) of the file.
+    "downloadUri": "A String", # Output only. The download URL which should be used to allow a human user to download the attachment. Bots should not use this URL to download attachment content.
+    "source": "A String", # The source of the attachment.
+    "name": "A String", # Resource name of the attachment, in the form "spaces/*/messages/*/attachments/*".
   }</pre>
 </div>