Update Node in Travis

Author: wooorm

.travis.yml

@@ -1,7 +1,7 @@
 language: node_js
 node_js:
 - '4.0'
-- '8.0'
+- '9.0'
 after_script: bash <(curl -s https://codecov.io/bash)
 deploy:
   - provider: npm
@@ -10,7 +10,7 @@ deploy:
       secure: Tvys9puncttZicY3RDRQdfaiqjA50S4kXN0VO5y61GZnXA9jqqkII7z76OeJxzPq0Bp8UUHMOA+Lf8iGMowkLUuexE/a1tzLUMVIctskqMC1dJPEeKn1A1LOH3tkCJCe0Xs6bLF/XtJ0Sd/kVJjkGAAPS/erjYHZNNXv+ksQT1Y=
     on:
       tags: true
-      node: '4.0'
+      node: '9.0'
   - provider: releases
     api_key:
       secure: wwCPWGftSTLvwgxgGZCg39K9otbNDHj8slxffh/MTJT/pWYKnBqufQfe6WcCs06c5z6kTddKS7E/ao7jwVlB5/8pIlMzR9cSnCMpJtmh8mFJPSMEMuM4dOVuntNCS58iei7O3PZHuJmQxZY5r6Zrk2egAcsgsDzV6959rxrS3WI=
@@ -19,4 +19,4 @@ deploy:
       - "mdast-util-heading-range.min.js"
     on:
       tags: true
-      node: '8.0'
+      node: '9.0'