Update pbr from 3.0.0 to 3.1.1

Author: pyup-bot

{{cookiecutter.project_slug}}/requirements.txt

@@ -18,7 +18,7 @@ mock==2.0.0
 packaging==16.8
 parse==1.8.2
 parse-type==0.3.4
-pbr==3.0.0
+pbr==3.1.1
 pluggy==0.4.0
 py==1.4.33
 Pygments==2.2.0