software updates (Graylog2#718)

* Bump snowballstemmer from 1.9.0 to 1.9.1

Bumps [snowballstemmer](https://github.com/snowballstem/snowball) from 1.9.0 to 1.9.1.
- [Release notes](https://github.com/snowballstem/snowball/releases)
- [Commits](https://github.com/snowballstem/snowball/commits)

Signed-off-by: dependabot-preview[bot] <[email protected]>

* Bump certifi from 2019.3.9 to 2019.9.11

Bumps [certifi](https://github.com/certifi/python-certifi) from 2019.3.9 to 2019.9.11.
- [Release notes](https://github.com/certifi/python-certifi/releases)
- [Commits](certifi/python-certifi@2019.03.09...2019.09.11)

Signed-off-by: dependabot-preview[bot] <[email protected]>

* Bump packaging from 19.1 to 19.2

Bumps [packaging](https://github.com/pypa/packaging) from 19.1 to 19.2.
- [Release notes](https://github.com/pypa/packaging/releases)
- [Changelog](https://github.com/pypa/packaging/blob/master/CHANGELOG.rst)
- [Commits](pypa/packaging@19.1...19.2)

Signed-off-by: dependabot-preview[bot] <[email protected]>

* Bump urllib3 from 1.25.3 to 1.25.6

Bumps [urllib3](https://github.com/urllib3/urllib3) from 1.25.3 to 1.25.6.
- [Release notes](https://github.com/urllib3/urllib3/releases)
- [Changelog](https://github.com/urllib3/urllib3/blob/master/CHANGES.rst)
- [Commits](urllib3/urllib3@1.25.3...1.25.6)

Signed-off-by: dependabot-preview[bot] <[email protected]>

requirements.txt

@@ -3,7 +3,7 @@ argh==0.26.2
 Babel==2.7.0
 backports-abc==0.5
 backports.ssl-match-hostname==3.7.0.1
-certifi==2019.3.9
+certifi==2019.9.11
 chardet==3.0.4
 docutils==0.15.2
 futures==3.1.1
@@ -12,7 +12,7 @@ imagesize==1.1.0
 Jinja2==2.10.1
 livereload==2.6.1
 MarkupSafe==1.1.1
-packaging==19.1
+packaging==19.2
 pathtools==0.1.2
 port-for==0.3.1
 Pygments==2.4.2
@@ -22,12 +22,12 @@ PyYAML==5.1.2
 requests==2.22.0
 singledispatch==3.4.0.3
 six==1.12.0
-snowballstemmer==1.9.0
+snowballstemmer==1.9.1
 Sphinx==2.2.0
 sphinx-autobuild==0.7.1
 sphinx-rtd-theme==0.4.3
 sphinxcontrib-websupport==1.1.2
 tornado==5.1.1
 typing==3.7.4
-urllib3==1.25.3
+urllib3==1.25.6
 watchdog==0.9.0