Update specs to new rspec syntax

spec/features/user_sign_in_spec.rb

@@ -4,7 +4,7 @@ feature 'User sign in' do
   scenario 'redirects to the home page when not signed in' do
     visit root_path
 
-    current_path.should == new_session_path
+    expect(current_path).to eq new_session_path
   end
 
   scenario 'signs the user in' do
@@ -15,6 +15,6 @@ feature 'User sign in' do
     fill_in 'Password', with: user.password
     click_button 'Sign in'
 
-    current_path.should == root_path
+    expect(current_path).to eq root_path
   end
 end