Apply Layout/LineLength rubocop rule

Note we're excluding a few files:

* Configuration files that weren't generated by us
* Migration files that weren't generated by us
* The Gemfile, since it includes an important comment that must be on
  the same line as the gem declaration
* The Budget::Stats class, since the heading statistics are a mess and
  having shorter lines would require a lot of refactoring

spec/models/ahoy/data_source_spec.rb

@@ -30,7 +30,9 @@ describe Ahoy::DataSource do
       ds = Ahoy::DataSource.new
       ds.add "foo", Ahoy::Event.where(name: "foo").group_by_day(:time).count
       ds.add "bar", Ahoy::Event.where(name: "bar").group_by_day(:time).count
-      expect(ds.build).to eq :x => ["2015-01-01", "2015-01-02", "2015-01-03"], "foo" => [2, 1, 0], "bar" => [1, 0, 2]
+      expect(ds.build).to eq :x => ["2015-01-01", "2015-01-02", "2015-01-03"],
+                             "foo" => [2, 1, 0],
+                             "bar" => [1, 0, 2]
     end
   end
 end