Allow twitch-cli to open default browser in Windows when run inside WSL

[3ventic]

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

Problem/Feature

twitch token -u does not open the browser from WSL. Call Windows to open the browser, when inside WSL.

Description of Changes:

• Split openBrowser's linux logic to WSL and "real" Linux specific commands
• Add errcheck to openBrowser and print the URL in the console, if opening the browser fails

Checklist

• My code follows the Contribution Guide
• I have self-reviewed the changes being requested
• I have made comments on pieces of code that may be difficult to understand for other editors
• I have updated the documentation (if applicable)

[lleadbet]

lgtm, thanks for fixing this.