ci(travis): improves build speed (#294)

Author: juancarlostong

.travis.yml

@@ -17,19 +17,17 @@ stages:
 jobs:
   include:
     - stage: 'Lint markdown files'
-      language: ruby
-      rvm: 2.4.1
       os: linux
+      language: generic
       install: gem install awesome_bot
       script:
         - find . -type f -name '*.md' -exec awesome_bot {} \;
       notifications:
         email: false
 
     - stage: 'Lint markdown files'
-      language: node_js
-      node_js: 12
       os: linux
+      language: generic
       before_install: skip
       install:
         - npm i -g markdown-spellcheck