Merge pull request rspec#2137 from maclover7/patch-2

Fix typo

Author: JonRowe

DEV-README.md

@@ -20,7 +20,7 @@ Or ...
     bundle install --binstubs
     bin/rspec
 
-## Customize the dev enviroment
+## Customize the dev environment
 
 The Gemfile includes the gems you'll need to be able to run specs. If you want
 to customize your dev enviroment with additional tools like guard or