Bump trio from 0.11.0 to 0.12.1

Bumps [trio](https://github.com/python-trio/trio) from 0.11.0 to 0.12.1.
- [Release notes](https://github.com/python-trio/trio/releases)
- [Commits](python-trio/trio@v0.11.0...v0.12.1)

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

Author: dependabot-preview[bot]

requirements.txt

@@ -7,4 +7,4 @@ pytest-trio==0.5.2; python_version>="3.6"
 pytest==4.5.0
 six==1.12.0
 tornado>=5.0
-trio==0.11.0; python_version>="3.6"
+trio==0.12.1; python_version>="3.6"