Fix Rubocop violations after bumping rubocop-govuk

from 4.18.0 to 5.0.1

spec/features/http_request_handling_spec.rb

@@ -44,7 +44,7 @@ def app
     describe "#location" do
       subject { super().location }
 
-      it { is_expected.to eq(nil) }
+      it { is_expected.to be_nil }
     end
 
     specify { expect(last_response.headers).not_to include("Cache-Control") }
@@ -252,7 +252,7 @@ def app
     describe "#location" do
       subject { super().location }
 
-      it { is_expected.to eq(nil) }
+      it { is_expected.to be_nil }
     end
   end
 
@@ -830,7 +830,7 @@ def app
     describe "#location" do
       subject { super().location }
 
-      it { is_expected.to eq(nil) }
+      it { is_expected.to be_nil }
     end
   end
 
@@ -1147,7 +1147,7 @@ def app
         describe "#location" do
           subject { super().location }
 
-          it { is_expected.to eq(nil) }
+          it { is_expected.to be_nil }
         end
       end
     end
@@ -1285,7 +1285,7 @@ def app
         describe "#location" do
           subject { super().location }
 
-          it { is_expected.to eq(nil) }
+          it { is_expected.to be_nil }
         end
       end
     end

spec/performance/benchmark_spec.rb

@@ -1,7 +1,7 @@
 require_relative "../../boot"
 require_relative "../../lib/benchmark/all"
 
-describe "Benchmarking", performance: true do
+describe "Benchmarking", :performance do
   include Rack::Test::Methods
 
   def app
@@ -10,7 +10,7 @@ def app
 
   let(:number_of_runs) { ENV["NUMBER_OF_RUNS"] || 1000 }
 
-  it "generates timings for no host, 301, 410, 404" do
+  it "generates timings for no host, 301, 410, 404" do # rubocop:disable RSpec/NoExpectationExample
     Benchmark::All.new(number_of_runs).run!
   end
 end

spec/units/bouncer/canonicalized_request_spec.rb

@@ -8,7 +8,7 @@
 
     it "returns true if valid URI passed" do
       canonicalized_request = described_class.new(env)
-      allow(canonicalized_request).to receive(:bluri).and_return(instance_double("Rack::Request"))
+      allow(canonicalized_request).to receive(:bluri).and_return(instance_double(Rack::Request))
       expect(canonicalized_request.valid?).to be(true)
     end