explicitly specify the distro to get py26 and py33

tomato42 · tomato42 · commit 091ca06422fc · 2019-09-27T17:51:41.000+02:00
diff --git a/.travis.yml b/.travis.yml
@@ -1,3 +1,6 @@
+# workaround for 3.7 not available in default configuration
+# travis-ci/travis-ci#9815
+dist: trusty
 sudo: false
 language: python
 cache: pip
