Bump trio from 0.12.1 to 0.13.0 (#151)

Bumps [trio](https://github.com/python-trio/trio) from 0.12.1 to 0.13.0.
- [Release notes](https://github.com/python-trio/trio/releases)
- [Commits](python-trio/trio@v0.12.1...v0.13.0)

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

Author: dependabot-preview[bot]

requirements.txt

@@ -9,6 +9,6 @@ pytest==5.2.2; python_version>="3.5"
 six==1.13.0
 tornado==5.1.1; python_version<"3.6"
 tornado==6.0.3; python_version>="3.6"
-trio==0.12.1; python_version>="3.6"
+trio==0.13.0; python_version>="3.6"
 outcome==1.0.1; python_version>="3.5"
 attrs==19.3.0; python_version>="3.5"