Files with syntax errors are ignored

`cypress run` ignores files with syntax errors and the tests pass without any indication of a problem. The tests should fail instead.

Also when you run tests on a single file with syntax errors `cypress run --spec file.js`, cypress just displays the message "Tests should begin momentarily..." and hangs.

```
$ cypress version
Cypress CLI: 0.12.0
Cypress App: 0.17.10
```