chore(ci): re-enable tests on Windows (#5637)

* chore: Add Windows to Travis

This commit runs the unit tests on Windows.

There are two tests failing on Windows that we skip.

I spoke to Mathias B and we agreed to
defer debugging this for now in favour of getting tests running on
Windows. But we didn't want to ignore it forever, hence giving the test
a date at which it will start to fail.

.travis.yml

@@ -13,6 +13,17 @@ cache:
     - node_modules
 jobs:
   include:
+    - os: "windows"
+      node_js: "10.19.0"
+      env:
+        - CHROMIUM=true
+      before_install:
+        # populate .local-firefox for launcher tests
+        - PUPPETEER_PRODUCT=firefox npm install
+      script:
+        - ls .local-chromium .local-firefox
+        - npm run tsc
+        - npm run unit
     - node_js: "10.19.0"
       dist: trusty
       env: