Land rapid7#5317, update to ruby 2.1.6

Author: Brent Cook

.ruby-version

@@ -1 +1 @@
-2.1.5
+2.1.6

.travis.yml

@@ -25,7 +25,7 @@ script:
   - git diff --exit-code && bundle exec rake $RAKE_TASKS
 sudo: false
 rvm:
-  - '2.1'
+  - '2.1.6'
 
 notifications:
   irc: "irc.freenode.org#msfnotify"
@@ -40,4 +40,4 @@ branches:
     - metakitty
 
 addons:
-  postgresql: '9.3'
+  postgresql: '9.3'