Suggestion: Smarter subject stub cop

[andyw8]

I wonder if it would be feasible to checking for stubbing the SUT even when subject isn't used, e.g.:

it "..." do
  loan = Foo.new
  allow(loan).to receive(:bar).and_return(:baz)
  expect(loan.bar).to eq(:baz)
end

[Darhazer]

Related to #311