Merge pull request #1106 from python-trio/dependabot/pip/importlib-metadata-0.18

Author: dependabot-preview[bot]

test-requirements.txt

@@ -18,7 +18,7 @@ entrypoints==0.3          # via flake8
 flake8==3.7.7
 idna==2.8
 immutables==0.9
-importlib-metadata==0.17  # via pluggy, pytest
+importlib-metadata==0.18  # via pluggy, pytest
 ipython-genutils==0.2.0   # via traitlets
 ipython==7.5.0
 isort==4.3.20             # via pylint