ci: adding travis file with Greenkeeper and semantic-release enabled

.travis.yml

@@ -2,20 +2,20 @@ language: node_js
 cache:
   directories:
     - node_modules
-    - ~/.npm
 notifications:
   email: false
 node_js:
   - '8'
   - '7'
 before_script:
-  - greenkeeper-lockfile-update
   - npm prune
+  - greenkeeper-lockfile-update
 after_success:
   - npm run semantic-release
 branches:
   except:
     - /^v\d+\.\d+\.\d+$/
 before_install:
-  - npm install -g npm@5
-  - npm install -g greenkeeper-lockfile@1
+- npm install -g npm@5
+- npm install -g greenkeeper-lockfile@1
+after_script: greenkeeper-lockfile-upload