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/helpers/application_helper_spec.rb

@@ -3,19 +3,19 @@ require 'rails_helper'
 describe ApplicationHelper do
 
   describe "#author_of?" do
-    it "should be true if user is the author" do
+    it "is true if user is the author" do
       user = create(:user)
       proposal = create(:proposal, author: user)
       expect(author_of?(proposal, user)).to eq true
     end
 
-    it "should be false if user is not the author" do
+    it "is false if user is not the author" do
       user = create(:user)
       proposal = create(:proposal)
       expect(author_of?(proposal, user)).to eq false
     end
 
-    it "should be false if user or authorable is nil" do
+    it "is false if user or authorable is nil" do
       user = create(:user)
       proposal = create(:proposal)