Fix test coverage reports

[remojansen]

The cov reports are not working. More info at inversify/inversify-express-utils#41 (comment)

[dcavanagh]

The problem is with gulp-mocha ^4.0. sindresorhus/gulp-mocha#159
I tried reverting gulp-mocha to ^3.0 and the code coverage worked again.

[lholznagel]

Just as a general idea and to prevent things like this, maybe we should lock the dependency versions? I mean we have greenkeeper enabled.

[remojansen]

@lholznagel I know but this is an odd one because 3.0 and 4.0 is a breaking change. But the build is successful and the coverage reports are not available :(

[dcavanagh]

@remojansen What if you check that the coverage report is not empty?
This fails the build

var report = require('./coverage/coverage-final.json');
    if (Object.keys(report).length === 0) {
        throw new Error("no test coverage");
    }
    return ret;

[remojansen]

@AltekkeE That sounds like a good way to prevent this issue in the future. Thanks for sharing it 👍

[remojansen]

Rolled back to 3.0.1 will wait until gulp-mocha fixes the problems.