Rename Recipient.CLASS to Recipient.STREAM.

(imported from commit a530194163f7260c73921137fa1ff671f14516f6)

tools/post-receive

@@ -43,7 +43,7 @@ def process_push(oldrev, newrev, refname):
                            oldrev, newrev, refname])
     commits = subprocess.check_output(["git", "log", "--reverse", "--pretty=- **%aN**: %s", "%s..%s" % (oldrev, newrev)])
     message_data = {
-        "type": "class",
+        "type": "stream",
         "class": "test" if refname == "refs/heads/test-post-receive" else "devel",
         "instance": "commits",
         "content": "The following commits were just pushed to `%s`:\n\n"