Switch over to npm@5

Author: timdorr

.travis.yml

@@ -1,9 +1,10 @@
 language: node_js
 node_js:
   - "node"
+before_install:
+  - npm i -g npm
 script:
   - npm run lint
   - npm run test:cov
 after_success:
   - npm run coverage
-cache: yarn