travis: use py367 on macOS to get a python build with openssl1.1

.travis/install.sh

@@ -33,8 +33,8 @@ if [[ "$(uname -s)" == 'Darwin' ]]; then
             pyenv global 3.5.3
             ;;
         py36)
-            pyenv install 3.6.0
-            pyenv global 3.6.0
+            pyenv install 3.6.7  # minimum for homebrew to select openssl 1.1.x
+            pyenv global 3.6.7
             ;;
     esac
     pyenv rehash