Remove `should' usages in specs

spec/models/user_spec.rb

@@ -1,17 +1,17 @@
 describe User do
   subject(:user) { FactoryGirl.build(:user) }
 
-  it { should be_valid }
-  it { should have_many :playlists }
-  it { should validate_presence_of :email }
-  it { should validate_presence_of :password }
-  it { should validate_presence_of :password_hash }
+  it { is_expected.to be_valid }
+  it { is_expected.to have_many :playlists }
+  it { is_expected.to validate_presence_of :email }
+  it { is_expected.to validate_presence_of :password }
+  it { is_expected.to validate_presence_of :password_hash }
 
   context 'when a user with the same email address already exists' do
     let(:old_user)  { FactoryGirl.create(:user, email: 'unique@example.net') }
     subject(:user)  { FactoryGirl.build(:user, email: old_user.email) }
 
-    it { should_not be_valid }
+    it { is_expected.to_not be_valid }
 
     it 'has an error on email attribute' do
       user.valid?
@@ -22,7 +22,7 @@ describe User do
   context 'when password_confirmation does not match password' do
     before { user.password_confirmation = user.password + 'INVALID' }
 
-    it { should_not be_valid }
+    it { is_expected.to_not be_valid }
   end
 
   describe '#password=' do