Record coverage information during spec runs

We want to start improving our test coverage. In order to do that, we
should be reporting coverage information to Coveralls for Travis builds,
otherwise we should display it in the console when developing locally.

Author: sds

Diff for: .gitignore

@@ -1,5 +1,6 @@
 .bundle
 Gemfile.lock
+/coverage
 /pkg
 
 # YARD

Diff for: .simplecov

@@ -0,0 +1,4 @@
+SimpleCov.start do
+  add_filter '/bin/'
+  add_filter '/spec/'
+end

Diff for: Gemfile

@@ -8,3 +8,5 @@ gem 'overcommit', '0.26.0'
 # Pin tool versions (which are executed by Overcommit) for Travis builds
 gem 'rubocop', '0.32.1'
 gem 'travis', '~> 1.7'
+
+gem 'coveralls'

Diff for: spec/spec_helper.rb

@@ -1,3 +1,13 @@
+if ENV['TRAVIS']
+  # When running in Travis, report coverage stats to Coveralls.
+  require 'coveralls'
+  Coveralls.wear!
+else
+  # Otherwise render coverage information in coverage/index.html and display
+  # coverage percentage in the console.
+  require 'simplecov'
+end
+
 require 'scss_lint'
 
 Dir[File.dirname(__FILE__) + '/support/**/*.rb'].each { |f| require f }