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/models/proposal_notification_spec.rb

@@ -3,21 +3,21 @@ require 'rails_helper'
 describe ProposalNotification do
   let(:notification) { build(:proposal_notification) }
 
-  it "should be valid" do
+  it "is valid" do
     expect(notification).to be_valid
   end
 
-  it "should not be valid without a title" do
+  it "is not valid without a title" do
     notification.title = nil
     expect(notification).to_not be_valid
   end
 
-  it "should not be valid without a body" do
+  it "is not valid without a body" do
     notification.body = nil
     expect(notification).to_not be_valid
   end
 
-  it "should not be valid without an associated proposal" do
+  it "is not valid without an associated proposal" do
     notification.proposal = nil
     expect(notification).to_not be_valid
   end
@@ -50,7 +50,7 @@ describe ProposalNotification do
       Setting[:proposal_notification_minimum_interval_in_days] = 3
     end
 
-    it "should not be valid if below minium interval" do
+    it "is not valid if below minium interval" do
       proposal = create(:proposal)
 
       notification1 = create(:proposal_notification, proposal: proposal)
@@ -60,7 +60,7 @@ describe ProposalNotification do
       expect(notification2).to_not be_valid
     end
 
-    it "should be valid if notifications above minium interval" do
+    it "is valid if notifications above minium interval" do
       proposal = create(:proposal)
 
       notification1 = create(:proposal_notification, proposal: proposal, created_at: 4.days.ago)
@@ -70,7 +70,7 @@ describe ProposalNotification do
       expect(notification2).to be_valid
     end
 
-    it "should be valid if no notifications sent" do
+    it "is valid if no notifications sent" do
       notification1 = build(:proposal_notification)
 
       expect(notification1).to be_valid