Update dependencies, remove old node versions (#54)

Author: jorrit

.gitignore

@@ -4,3 +4,4 @@ npm-debug.log
 coverage
 .idea
 test/tmp
+.nyc_output

.travis.yml

@@ -1,12 +1,12 @@
 language: node_js
 node_js:
-  - 6
-  - 8
   - 10
   - 12
+  - 14
 before_install:
   - npm install -g npm@latest
-  - npm install -g greenkeeper-lockfile@1
-before_script: greenkeeper-lockfile-update
-after_script: greenkeeper-lockfile-upload
-script: npm run lint && npm run test-coveralls
+script:
+  - npm run lint
+  - npm run test
+after_success:
+  - npm run coverage