Support python3.7 (#645)

* Support python3.7

* add 3.7 env to travis

.travis.yml

@@ -1,8 +1,8 @@
 language: python
-python:
-  - "3.6"
+dist: xenial
+sudo: required
 node_js:
-  - "8"
+  - 8
 cache:
   pip: true
 install:
@@ -15,14 +15,12 @@ install:
 
 jobs:
   include:
-  - name: "Branch Tests"
-    script:
-      - set -eo pipefail
-      - flake8 server
-      - black --check
-      - npm run --prefix client/ build
-      - npm run --prefix client/ unit-test
-      - pytest -s server/test
+  - name: "Branch Tests 3.7"
+    python: "3.7"
+    script: ./travis-build.sh
+  - name: "Branch Tests 3.6"
+    python: "3.6"
+    script: ./travis-build.sh
   - name: "Smoke Tests"
     if: branch = master AND type = cron
     script: