travis: update versions, force travis to use node 10

.travis.yml

@@ -1,12 +1,18 @@
-dist: xenial
-sudo: true
+version: ~> 1.0
+
+os: linux
+dist: bionic
+
 language: python
 python:
     - 3.6
     - 3.7
-    - 3.7-dev
+    - 3.8
+    - 3.9-dev
 install:
     - pip install -r requirements.txt -r requirements-dev.txt
+    - nvm install 10
+    - nvm use 10
     - npm install
 script:
     - pytest --cov=.