Update hacking for Python3

The repo is Python 3 now, so update hacking to version 3.0 which
supports Python 3.

Fix:
W605 invalid escape sequence

Change-Id: Id55815b07d2355983a1ba97565f2473fdd49f4b3

test-requirements.txt

@@ -2,5 +2,5 @@
 # of appearance. Changing the order has an impact on the overall integration
 # process, which may cause wedges in the gate later.
 
-hacking>=0.10.0,<0.11
+hacking>=3.0,<3.1.0 # Apache-2.0
 stestr>=2.0.0 # Apache-2.0

tests/test_titles.py

@@ -84,7 +84,7 @@ class TestTitles(testtools.TestCase):
             if line.startswith("..") and "image::" in line:
                 continue
             # Allow lines which do not contain any whitespace
-            if re.match("\s*[^\s]+$", line):
+            if re.match(r"\s*[^\s]+$", line):
                 continue
             self.assertTrue(
                 len(line) < 80,