Remove TravisCI settings not needed with Node.js 8

.travis.yml

@@ -7,17 +7,13 @@ node_js:
   - 8
 matrix:
   fast_finish: true
-env:
-  global:
-    - BUILD_LEADER_ID=2
 script: npm run travis
 before_install:
-  - npm i -g npm@^3.0.0
+  - npm i -g npm
 before_script:
   - npm prune
 after_success:
-  - npm install -g npx
-  - npx -p node@8 npm run semantic-release
+  - npm run semantic-release
 branches:
   except:
     - /^v\d+\.\d+\.\d+$/