Update to a newer hacking library

The older hacking library has a cap on pbr <2.0, with the recent 2.0.0
release of PBR it's causing failures in the pep8 job.

hacking isn't kept in sync via the typical proposal-bot updates.

Do it manually to clear the gate issue.

pep8 runtests: commands[0] | flake8
./os_collect_config/merger.py:45:22: W292 no newline at end of file
    return final_list

Change-Id: If863d2e190a4e1701ebf1fcb99a783075cda2556
Related-Bug: #1668848

os_collect_config/merger.py

@@ -42,4 +42,4 @@ def merged_list_from_content(final_content, deployment_keys, collector_name):
                     final_list.append((deployment['name'],
                                        deployment['config']))
     final_list.insert(0, (collector_name, final_content))
-    return final_list
+    return final_list

test-requirements.txt

@@ -1,7 +1,7 @@
 # The order of packages is significant, because pip processes them in the order
 # of appearance. Changing the order has an impact on the overall integration
 # process, which may cause wedges in the gate later.
-hacking<0.10,>=0.9.2
+hacking>=0.12.0,!=0.13.0,<0.14 # Apache-2.0
 
 coverage>=4.0 # Apache-2.0
 fixtures>=3.0.0 # Apache-2.0/BSD