build(TravisCI): remove greenkeeper lockfile

.travis.yml

@@ -1,5 +1,5 @@
 os: osx
-osx_image: xcode9.4
+osx_image: xcode10
 
 language: node_js
 node_js:
@@ -8,15 +8,8 @@ cache:
   directories:
     - "node_modules"
 
-before_install:
-  - npm install -g greenkeeper-lockfile
-
 before_script:
   - swiftlint version
-  - greenkeeper-lockfile-update
 
 script:
   - npm run lint
-
-after_script:
-  - greenkeeper-lockfile-upload