Bump pytest-selenium from 1.15.1 to 1.16.0 (#328)

Bumps [pytest-selenium](https://github.com/pytest-dev/pytest-selenium) from 1.15.1 to 1.16.0.
- [Release notes](https://github.com/pytest-dev/pytest-selenium/releases)
- [Changelog](https://github.com/pytest-dev/pytest-selenium/blob/master/docs/news.rst)
- [Commits](https://github.com/pytest-dev/pytest-selenium/compare/v1.15.1...v1.16.0)

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

requirements/py27-tests.txt

@@ -5,6 +5,6 @@ pypom==2.2.0
 pytest==4.2.1
 pytest-fxa==1.4.0
 pytest-metadata==1.8.0
-pytest-selenium==1.15.1
+pytest-selenium==1.16.0
 pytest-xdist==1.26.1
 selenium==3.141.0

requirements/py36-tests.txt

@@ -4,6 +4,6 @@ pypom==2.2.0
 pytest==4.2.1
 pytest-fxa==1.4.0
 pytest-metadata==1.8.0
-pytest-selenium==1.15.1
+pytest-selenium==1.16.0
 pytest-xdist==1.26.1
 selenium==3.141.0