Add 'm' gem for running a single test by giving the line number

Gemfile

@@ -8,4 +8,5 @@ gem "airbrake"
 group :test do
   gem 'rake'
   gem 'purdytest', :require => false
+  gem 'm'
 end

Gemfile.lock

@@ -12,6 +12,10 @@ GEM
     builder (3.1.3)
     eventmachine (0.12.10)
     i18n (0.6.1)
+    m (1.2.1)
+      method_source (>= 0.6.7)
+      rake (>= 0.9.2.2, < 1.0.0)
+    method_source (0.8)
     minitest (2.10.0)
     multi_json (1.3.6)
     purdytest (1.0.0)
@@ -45,6 +49,7 @@ PLATFORMS
 
 DEPENDENCIES
   airbrake
+  m
   purdytest
   rake
   riak-client