converted to yarn

which is SO much faster than npm
* also updated to latest tools, which fixed build issues.
Note: "grunt-sass": "2.1.0" IS REQUIRED as 3.0.0/3.0.1 gives errors I wasn't able to fix
(see sourcey/spectacle#156)

Author: Alain Dumesny

.travis.yml

@@ -6,25 +6,25 @@ sudo: required
 addons:
   chrome: stable
 #before_install:
-#- npm install -g protractor@3.3.0
+#- yarn global add protractor@3.3.0
 cache:
   directories:
     - node_modules
 install:
-#- npm install -g npm@6.0.1
-- npm install -g grunt-cli
-- npm install -g bower
-#- npm install selenium-webdriver
-- npm install
+#- yarn global add npm@6.0.1
+- yarn global add grunt-cli
+- yarn global add bower
+#- yarn add selenium-webdriver
+- yarn
 - bower install
 #- ./node_modules/protractor/bin/webdriver-manager update --standalone
 #before_script:
 #- export CHROME_BIN=chromium-browser
 #- export DISPLAY=:99.0
 #- sh -e /etc/init.d/xvfb start
 script:
-- npm run build
-- npm test
+- yarn build
+- yarn test
 # - grunt e2e-test
 notifications:
   slack: