chore: remove greenkeeper-lockfile plugin (not needed anymore)

Author: Evgeny Barabanov

.travis.yml

@@ -29,7 +29,6 @@ addons:
       - xvfb
 before_install:
   - npm i -g yarn@1
-  - yarn global add greenkeeper-lockfile@2
 install:
   - yarn
   - export DISPLAY=':99.0'
@@ -39,8 +38,6 @@ before_script:
   - export DISPLAY=:99.0
   - sh -e /etc/init.d/xvfb start &
   - sleep 3
-  - greenkeeper-lockfile-update
-after_script: greenkeeper-lockfile-upload
 script:
   - yarn dist
   - if [[ "$TRAVIS_OS_NAME" == "osx" ]]; then sudo hdiutil attach ./build-artifacts/ElectronAngularNativeApp.dmg; fi