Update pbr from 5.3.0 to 5.3.1

requirements/prod.txt

@@ -286,9 +286,9 @@ nobot==0.5 \
     --hash=sha256:fa0582d81f562cd5b61e241005feb3f51548fe3fc165aed292952ff78676e28a \
     --hash=sha256:0a1c43a74f1c55f06cf2eb98cb472762dbdd7df5eb693d438c9fb42cfcfe79e5
 # pbr is required by mock
-pbr==5.3.0 \
-    --hash=sha256:089ccb087e9bd8f278caedfa6c2c5d461381437eda3db750b6834e78b319f404 \
-    --hash=sha256:9fb1c3371344cd617eb073c6c00872e9b0e5a7fefed6cd29f327a1b26ab5c498
+pbr==5.3.1 \
+    --hash=sha256:9181e2a34d80f07a359ff1d0504fad3a47e00e1cf2c475b0aa7dcb030af54c40 \
+    --hash=sha256:94bdc84da376b3dd5061aa0c3b6faffe943ee2e56fa4ff9bd63e1643932f34fc
 # polib is required by dennis
 polib==1.1.0 \
     --hash=sha256:93b730477c16380c9a96726c54016822ff81acfa553977fdd131f2b90ba858d7 \