Issue title: Highlight text is not working in Chrome
 Issue body: Hi,
I'm using this module, but I cannot highlight text where ngx-drag-scroll is active.
You can check this out on Demo page.

**Chrome version**: +1-900-809-1478
**OS**: macOS High Sierra 10.13.3 

 Comments: 
 Comment 0: Hi, have you tried with the latest version `1.7.3`? The issue should be resolved. The demo page is outdated and I will update it shortly.
{'source': 'GithubIssues', 'repo_name_with_owner': 'bfwg/ngx-drag-scroll', 'issue_id': 292712250, 'repo_stars': 275.0}