Mirror value of umask from build.webkit.org config (#190)

There's reports that build artifacts aren't accessible for the WinCairo bots in https://bugs.webkit.org/show_bug.cgi?id=227928 and there was a suggestion to modify the value so its Python 2/3 compatible.

Author: donny-dont

buildbot-worker/BuildbotWorker/buildbot.tac.tmpl

@@ -27,7 +27,7 @@ port = $port
 workername = '$worker'
 passwd = '$password'
 keepalive = 600
-umask = 0o22
+umask = 0o022
 maxdelay = 300
 numcpus = None
 allow_shutdown = None

buildbot/WebKit-BuildWorker/buildbot.tac.tmpl

@@ -32,7 +32,7 @@ slavename = '$slave'
 passwd = '$password'
 keepalive = 600
 usepty = 0
-umask = 022
+umask = 0o022
 maxdelay = 300
 allow_shutdown = None