TEST: Set up for testing via zuul/sauce labs (#86)

This requires the .travis.yml to be updated with the open sauce credentials
as explained at https://github.com/defunctzombie/zuul/wiki/Travis-ci#5-final-step

.zuul.yml

@@ -0,0 +1,28 @@
+ui: tape
+browsers:
+  - name: chrome
+    version: latest
+    os: 'Mac 10.11'
+  - name: internet explorer
+    version: 9..11
+    os: 'Windows 10'
+  - name: firefox
+    version: latest
+    os: 'Mac 10.11'
+  - name: microsoftedge
+    version: latest
+  - name: safari
+    version: latest
+    os: 'Mac 10.11'
+  - name: iphone
+    version: '8.4..9.2'
+  - name: android
+    version: '4.3..5.1'
+  - name: opera
+    version: latest
+    platform: 'Windows 10'
+browserify:
+  - transform:
+      name: es2020
+      global: true
+  - transform: sheetify/transform