Allow to specify Sauce Connect Proxy Version

This enhancement allows it to specify the Sauce Connect Proxy version during runtime, e.g.:

$ sl sc --sc-version 4.5.4 --region eu

This allows to debug issues around specific Sauce Connect version without having to manually download them.

Commits:

• Allow specifying a Sauce Connect version (#82) 0fe3458
• downgrade eslint to v6.8 to support Node v8 c76a26e
• use tunnel-identifier as sauce connect example param 4dfaa07
• update readme ebf43c3

v4.1.0...v4.2.0