Remove node 7 from testing. Try removing package-lock.json because Travis is having problems

Author: drewpc

.travis.yml

@@ -4,10 +4,10 @@ node_js:
   - "10"
   - "9"
   - "8"
-  - "7"
   - "6"
 before_install:
   - npm install -g 'npm@^6.4.0'
+  - rm package-lock.json
 before_script:
   - npm run lint
   - npm run build