Bump cornice from 3.3.0 to 3.5.1

Bumps [cornice](https://github.com/mozilla-services/cornice) from 3.3.0 to 3.5.1.
- [Release notes](https://github.com/mozilla-services/cornice/releases)
- [Changelog](https://github.com/Cornices/cornice/blob/master/CHANGES.txt)
- [Commits](Cornices/cornice@3.3.0...3.5.1)

Signed-off-by: dependabot[bot] <support@dependabot.com>

requirements.txt

@@ -4,7 +4,7 @@ cffi==1.11.5
 chardet==3.0.4
 colander==1.5.1
 colorama==0.4.1
-cornice==3.3.0
+cornice==3.5.1
 cornice-swagger==0.7.0
 dockerflow==2018.4.0
 elasticsearch==6.3.1