Enable RSpec/NotToNot cop and fix all issues

Read about cop at http://www.rubydoc.info/gems/rubocop-rspec/RuboCop/Cop/RSpec/NotToNot

spec/models/verification/sms_spec.rb

@@ -9,14 +9,14 @@ describe Verification::Sms do
   it "validates uniqness of phone" do
     create(:user, confirmed_phone: "699999999")
     sms = described_class.new(phone: "699999999")
-    expect(sms).to_not be_valid
+    expect(sms).not_to be_valid
   end
 
   it "only allows spaces, numbers and the + sign" do
     expect(build(:verification_sms, phone: "0034 666666666")).to be_valid
     expect(build(:verification_sms, phone: "+34 666666666")).to be_valid
-    expect(build(:verification_sms, phone: "hello there")).to_not be_valid
-    expect(build(:verification_sms, phone: "555; DROP TABLE USERS")).to_not be_valid
+    expect(build(:verification_sms, phone: "hello there")).not_to be_valid
+    expect(build(:verification_sms, phone: "555; DROP TABLE USERS")).not_to be_valid
   end
 
 end