util: also silence py3 warnings from codec module

util: also silence py3 warnings from codec module

Fixes warnings like this:

+  mercurial/util.py:2446: DeprecationWarning: invalid escape sequence '\d'
+    return codecs.escape_decode(s)[0]

Differential Revision: https://phab.mercurial-scm.org/D2642

--- a/mercurial/util.py	Thu Feb 15 18:05:58 2018 -0800
+++ b/mercurial/util.py	Sun Mar 04 11:49:33 2018 -0500
@@ -249,6 +249,8 @@
     # silence warning emitted by passing user string to re.sub()
     warnings.filterwarnings(r'ignore', r'bad escape', DeprecationWarning,
                             r'mercurial')
+    warnings.filterwarnings(r'ignore', r'invalid escape sequence',
+                            DeprecationWarning, r'mercurial')
 
 def nouideprecwarn(msg, version, stacklevel=1):
     """Issue an python native deprecation warning