Add and apply RSpec/BeEq rubocop rule

This rule was added in rubocop-rspec 2.9.0. Once again, we were applying
it about 50% of the time.

spec/models/budget_spec.rb

@@ -241,7 +241,7 @@ describe Budget do
     it "returns nil if there is only one budget and it is still in drafting phase" do
       create(:budget, :drafting)
 
-      expect(Budget.current).to eq(nil)
+      expect(Budget.current).to be nil
     end
 
     it "returns the budget if there is only one and not in drafting phase" do
@@ -340,11 +340,11 @@ describe Budget do
     it "returns true if there is a winner investment" do
       budget.investments << build(:budget_investment, :winner, price: 3, ballot_lines_count: 2)
 
-      expect(budget.has_winning_investments?).to eq true
+      expect(budget.has_winning_investments?).to be true
     end
 
     it "hould return false if there is not a winner investment" do
-      expect(budget.has_winning_investments?).to eq false
+      expect(budget.has_winning_investments?).to be false
     end
   end
 
@@ -370,9 +370,9 @@ describe Budget do
       expect(publishing_prices_phase.next_phase).to eq(balloting_phase)
       expect(balloting_phase.next_phase).to eq(reviewing_ballots_phase)
       expect(reviewing_ballots_phase.next_phase).to eq(finished_phase)
-      expect(finished_phase.next_phase).to eq(nil)
+      expect(finished_phase.next_phase).to be nil
 
-      expect(informing_phase.prev_phase).to eq(nil)
+      expect(informing_phase.prev_phase).to be nil
       expect(accepting_phase.prev_phase).to eq(informing_phase)
       expect(reviewing_phase.prev_phase).to eq(accepting_phase)
       expect(selecting_phase.prev_phase).to eq(reviewing_phase)