Silence travis-ci build warnings by removing non-functional python3.6 (#4377)

* Remove non-functional python3.6 in travis env

* changelog

.travis.yml

@@ -72,5 +72,12 @@ matrix:
 install:
   - pip install tox
   
+  # if we don't have python3.6 in this environment, travis unhelpfully gives us
+  # a `python3.6` on our path which does nothing but spit out a warning. Tox
+  # tries to run it (even if we're not running a py36 env), so the build logs
+  # then have warnings which look like errors. To reduce the noise, remove the
+  # non-functional python3.6.
+  - ( ! command -v python3.6 || python3.6 --version ) &>/dev/null || rm -f $(command -v python3.6)
+
 script:
   - tox -e $TOX_ENV

changelog.d/4377.misc

@@ -0,0 +1 @@
+Silence travis-ci build warnings by removing non-functional python3.6