Replacing NPM with yarn in docs and build

.travis.yml

@@ -5,4 +5,4 @@ before_script:
   - "export DISPLAY=:99.0"
   - "sh -e /etc/init.d/xvfb start"
   - sleep 3
-script: npm test
+script: yarn test

README.md

@@ -14,11 +14,11 @@ Node is required for working with this site.
 
 To start with, install the necessary dependencies:
 
-    $ npm install
+    $ yarn install
 
 To start a development server, run:
 
-    $ npm start
+    $ yarn start
 
 This will build the site into the ./build directory, start a local start on port 8080, and begin watching the source files for modifications. The site will automatically be rebuilt when files are changed. Also, if you browser has the LiveReload extension, then the page will be reloaded.
 
@@ -26,7 +26,7 @@ These other gulp tasks are available:
 
     $ gulp docs # Build documentation into the ./docs directory
     $ gulp build # Build the site into the ./build directory
-    $ npm test # Run JSCS lint and Karma tests
+    $ yarn test # Run JSCS lint and Karma tests
 
 ## License