py3: byte-prefix sanitisation regexes in phabricator.py

So it doesn't die with "TypeError: cannot use a string pattern on a bytes-like
object".

Differential Revision: https://phab.mercurial-scm.org/D6863

hgext/phabricator.py

@@ -136,8 +136,8 b' def vcrcommand(name, flags, spec, helpca'
 
     def sanitiserequest(request):
         request.body = re.sub(
-            r'cli-[a-z0-9]+',
-            r'cli-hahayouwish',
+            br'cli-[a-z0-9]+',
+            br'cli-hahayouwish',
             request.body
         )
         return request