Update gem authors and emails

I've put a hefty amount of work into this project, and I don't think
anyone's going to mind me mentioning that.

Change-Id: Ifc07bac3e7fbf1168a6fde2272ac27d43ca808c4
Reviewed-on: http://gerrit.causes.com/35617
Reviewed-by: Shane da Silva <shane@causes.com>
Tested-by: Shane da Silva <shane@causes.com>

Author: sds

overcommit.gemspec

@@ -7,8 +7,8 @@ Gem::Specification.new do |s|
   s.license               = 'MIT'
   s.summary               = 'Git hook manager'
   s.description           = 'Utility to install, configure, and extend Git hooks'
-  s.authors               = ['Causes Engineering']
-  s.email                 = 'eng@causes.com'
+  s.authors               = ['Causes Engineering', 'Shane da Silva']
+  s.email                 = ['eng@causes.com', 'shane@causes.com']
   s.homepage              = 'http://github.com/causes/overcommit'
   s.post_install_message  =
     'Install hooks by running `overcommit --install` in your Git repository'