Drop yarn and greenkeeper

Author: RadValentin

.gitpod.yml

@@ -1,3 +1,3 @@
 tasks:
-  - init: yarn install
-  - command: yarn test
+  - init: npm install
+  - command: npm test

.travis.yml

@@ -1,11 +1,7 @@
-cache: yarn
 node_js:
   - node
   - 12
   - 10
 language: node_js
-script: "yarn test-travis"
-before_install: yarn global add greenkeeper-lockfile@1
-before_script: greenkeeper-lockfile-update
+script: "npm run test-travis"
 after_script: "npm install coveralls@2 && cat ./coverage/lcov.info | coveralls"
-after_script: greenkeeper-lockfile-upload