v0.15.5

Update isObservable to use the latest rxjs 6 definition. isObservable is public in v6 so once we upgrade to that we can use that instead of this custom implementation. This isObservable code is replacing an outdated version from the package is-observable.

Also eliminated warnTimeout delay in debounce and throttle tests since it was causing test completion to delay.

Removed codacy check since it has been problematic as of recently and causes problems for PR's.