change output of test-runner on compile error to adhere to the standard

[tehsphinx]

Fixes #11

[tehsphinx]

@ErikSchierboom: This change removes the extra test I created on a compile error to hold the error message and adds the error message on top level. The only output is then status and message. tests is null. Or should I omit that?

Example:

{
    "status": "error",
    "message": "./sample_test.go:37:1: missing return at end of function",
    "tests": null
}

[ErikSchierboom]

@tehsphinx Awesome! Could you make the tests an empty array perhaps?

[tehsphinx]

@ErikSchierboom

{
    "status": "error",
    "message": "./sample_test.go:37:1: missing return at end of function",
    "tests": []
}

[ErikSchierboom]

Thanks!