coverageMap is not an instance when using multiple test suites

[Cactusbone]

Using nightwatch '1.5.1' or '1.7.13', I was getting timeouts errors due to crash in afterEach (browser.globals.coverageReporter.coverageMap.merge undefined)

It seemed that coverageMap was a POJO when calling browser.collectCoverage (either during tests or during global afterEach).

to work around that, I set persist_globals to true, which did nothing, and ended up using a global beforeEach to restore the instance

        beforeEach(browser, done) {
            // fixes coverageMap not being the expected class instance
            browser.globals.coverageReporter.coverageMap = coverageReporter.coverageMap;
            done();
        },

I'm not too sure if that was expected to work out of the box, or is broken by some context, or if some version of nightwatch broke it.