Use latest npm.

Author: RubenVerborgh

.travis.yml

@@ -1,7 +1,7 @@
 sudo: false
 language: node_js
 node_js:
-  - "8.10"
+  - "8.0"
   - "10.0"
   - "node"
 env:
@@ -18,6 +18,9 @@ addons:
     - tim.localhost
     - nicola.localhost
 
+before_install:
+  - npm install -g npm@latest
+
 script:
   - npm run standard
   - npm run sonar