Removes spell check of md files stage from travis.yml (#446)

Author: mnoman09

.travis.yml

@@ -45,18 +45,6 @@ jobs:
       notifications:
         email: false
 
-    - stage: 'Lint markdown files'
-      os: linux
-      language: generic
-      before_install: skip
-      install:
-        - npm i -g markdown-spellcheck
-      before_script:
-        - wget --quiet https://raw.githubusercontent.com/optimizely/mdspell-config/master/.spelling
-      script:
-        - mdspell -a -n -r --en-us '**/*.md'
-      after_success: skip
-
     - stage: 'SourceClear and Lint'
       language: objective-c
       os: osx