Add tests on Python 3.9

Signed-off-by: Philippe Ombredanne <pombredanne@nexb.com>

Author: pombredanne

.travis.yml

@@ -1,3 +1,7 @@
+# This is a skeleton Travis CI config file that provides a starting point for adding CI
+# to a Python project. Since we primarily develop in python3, this skeleton config file
+# will be specific to that language.
+#
 # See https://config.travis-ci.com/ for a full list of configuration options.
 
 os: linux
@@ -9,9 +13,10 @@ python:
   - "3.6"
   - "3.7"
   - "3.8"
+  - "3.9"
 
 # Scripts to run at install stage
 install: ./configure
 
 # Scripts to run at script stage
-script: tmp/bin/pytest
+script: tmp/bin/pytest -vvs -n 2