The latest node 8 includes an updated npm already.

timdorr · josepot · commit d78eb87590da · 2018-09-21T23:18:49.000+02:00
diff --git a/.travis.yml b/.travis.yml
@@ -1,8 +1,6 @@
 language: node_js
 node_js:
   - "8"
-before_install:
-  - npm i -g npm
 script:
   - npm run lint
   - npm run test:cov
