Update tests for newer versions of should.js

[tomhughes]

[danielstjules]

Thanks for the PR! Looks like the jobs failed with several errors. You can run the full test suite yourself using make test-all or npm test

[tomhughes]

Think I've figured it out - there is an extra line in the stack traces now. Instead of:

      AssertionError: expected 'foo rar baz' to be 'foo bar baz'
      + expected - actual

      -foo rar baz
      +foo bar baz

      at Assertion.prop.(anonymous function) (node_modules/should/lib/should.js:61:14)
      at Context.<anonymous> (test/integration/fixtures/diffs/diffs.js:12:19)
      at callFn (lib/runnable.js:312:21)

we get:

      AssertionError: expected 'foo rar baz' to be 'foo bar baz'
      + expected - actual

      -foo rar baz
      +foo bar baz

      at Assertion.fail (node_modules/should/lib/assertion.js:91:17)
      at Assertion.Object.defineProperty.value (node_modules/should/lib/assertion.js:163:19)
      at Context.<anonymous> (test/integration/fixtures/diffs/diffs.js:12:19)
      at callFn (lib/runnable.js:312:21)

so we need to discard one more line when extracting the diff.

I've pushed an updated version that now passes.

[danielstjules]

Thanks! It's unfortunate that the trace is a bit noisier, but at least we'll be using a recent release :)