Avoid some npm issues (#154)

.travis.yml

@@ -1,6 +1,11 @@
 language: node_js
 notifications:
   email: false
+before_install: npm i -g npm@latest --no-audit
+install: npm config set progress=false && npm i --no-audit
+cache:
+  directories:
+  - node_modules
 stages:
 - name: check-pr
   if: type = pull_request