updating slimbar service to be Angular 6 compatible

[inunotaisho]

• What kind of change does this PR introduce? (Bug fix, feature, docs update, ...) Adding package.json changes to follow up to PR: https://github.com/akserg/ng2-slim-loading-bar/pull/68

• What is the current behavior? (You can also link to an open issue here)

  67 - where the library is still referring the RxJs module under wrong location when updated to RxJs v6

• What is the new behavior (if this is a feature change)? No behavior change except with testing 4 of the 16 test are not passing. Still trying to figure out why.

• Other information:

[devs4522]

@inunotaisho26 Is this PR still not completed ? When will it be done ?

[inunotaisho]

@devs4522 The issue faced with this PR is not with the package itself, but with the built Angular test. I haven't used them much to begin with, so I am not sure how to handle it.

I also haven't heard much from @akserg, so I am not sure if this project is still being maintained anymore.

[inunotaisho]

@devs4522 I did fork this project and was planning to maintain it because the nonprofit I work for as it uses it for its website. So, unlike this ng2-slim-loading-bar, if I can get the ball rolling, ngx-slim-loading-bar will have to be maintained so the nonprofit I work for can use it at all times. If you are interested, here is the url and if you'd like to help, drop in a PR.