Bump pytest from 4.6.4 to 5.1.2

Bumps [pytest](https://github.com/pytest-dev/pytest) from 4.6.4 to 5.1.2.
- [Release notes](https://github.com/pytest-dev/pytest/releases)
- [Changelog](https://github.com/pytest-dev/pytest/blob/master/CHANGELOG.rst)
- [Commits](pytest-dev/pytest@4.6.4...5.1.2)

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

Author: dependabot-preview[bot]

requirements/py27-tests.txt

@@ -2,7 +2,7 @@ mock==3.0.5
 mozlog==4.2.0
 pyfxa==0.7.3
 pypom==2.2.0
-pytest==4.6.4
+pytest==5.1.2
 pytest-fxa==1.4.0
 pytest-metadata==1.8.0
 pytest-selenium==1.16.0

requirements/py36-tests.txt

@@ -1,7 +1,7 @@
 mock==3.0.5
 pyfxa==0.7.3
 pypom==2.2.0
-pytest==4.6.4
+pytest==5.1.2
 pytest-fxa==1.4.0
 pytest-metadata==1.8.0
 pytest-selenium==1.16.0