Enables RSpec/ExampleWording and fixes all issues

Both avoiding 'should' and repiting 'it' on the tests description
improves reading them and also makes all descriptions consistent.

Read about cop at http://www.rubydoc.info/gems/rubocop-rspec/RuboCop/Cop/RSpec/ExampleWording

spec/controllers/admin/api/stats_controller_spec.rb

@@ -6,7 +6,7 @@ describe Admin::Api::StatsController do
     let(:user) { create(:administrator).user }
 
     context 'events or visits not present' do
-      it 'should respond with bad_request' do
+      it 'responds with bad_request' do
         sign_in user
         get :show
 
@@ -29,7 +29,7 @@ describe Admin::Api::StatsController do
         create :ahoy_event, name: 'bar', time: time_3
       end
 
-      it 'should return single events formated for working with c3.js' do
+      it 'returns single events formated for working with c3.js' do
         sign_in user
         get :show, events: 'foo'
 
@@ -39,7 +39,7 @@ describe Admin::Api::StatsController do
         expect(data).to eq "x" => ["2015-01-01", "2015-01-02"], "Foo" => [2, 1]
       end
 
-      it 'should return combined comma separated events formated for working with c3.js' do
+      it 'returns combined comma separated events formated for working with c3.js' do
         sign_in user
         get :show, events: 'foo,bar'
 
@@ -51,7 +51,7 @@ describe Admin::Api::StatsController do
     end
 
     context 'visits present' do
-      it 'should return visits formated for working with c3.js' do
+      it 'returns visits formated for working with c3.js' do
         time_1 = DateTime.parse("2015-01-01").in_time_zone
         time_2 = DateTime.parse("2015-01-02").in_time_zone
 
@@ -70,7 +70,7 @@ describe Admin::Api::StatsController do
     end
 
     context 'visits and events present' do
-      it 'should return combined events and visits formated for working with c3.js' do
+      it 'returns combined events and visits formated for working with c3.js' do
         time_1 = DateTime.parse("2015-01-01").in_time_zone
         time_2 = DateTime.parse("2015-01-02").in_time_zone
 
@@ -93,7 +93,7 @@ describe Admin::Api::StatsController do
     end
 
     context 'budget investments present' do
-      it 'should return budget investments formated for working with c3.js' do
+      it 'returns budget investments formated for working with c3.js' do
         time_1 = DateTime.parse("2017-04-01").in_time_zone
         time_2 = DateTime.parse("2017-04-02").in_time_zone