feat: screenshot testing (material-components#10)

Add screenshot testing with support for local and CI testing. Add Travis CI with support for unit tests, linting, and screenshot testing.

Author: patrickrodee

.gitignore

@@ -3,3 +3,6 @@ coverage
 node_modules
 .DS_Store
 *.iml
+*.snapshot.png
+*.diff.png
+key.json

.travis.yml

@@ -1,15 +1,28 @@
 language: node_js
-node_js: 8
-dist: trusty
-sudo: required
 git:
   depth: false
-branches:
-  only:
-    - experimental/travis
-addons:
-  chrome: stable
-install:
-  - npm i
-script:
-  - npm run test:ci
+
+dist: trusty
+sudo: required
+
+matrix:
+  include:
+    - node_js: 8
+      env: TEST_SUITE=unit
+      install: npm i
+      script: npm run test:unit-ci
+
+    - node_js: 8
+      env: TEST_SUITE=lint
+      install: npm i
+      script: npm run lint
+
+    - node_js: 8
+      env: TEST_SUITE=screenshots
+      install: npm i
+      script: 
+        - ./test/screenshot/start.sh
+        - sleep 10s
+        - npm run test:image-diff
+      after_script:
+        - COMMIT_HASH=$(git rev-parse --short HEAD) npm run upload:screenshots