Change scope of JUnit dependencies to test

[valfirst]

Description

JUnit dependencies are required for tests only. Previously there were classes requiring JUnit, but they were removed in https://github.com/saucelabs/saucerest-java/pull/443/files.

Motivation and Context

How Has This Been Tested?

Types of changes

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Refactoring (change which improves current code base; please describe the change)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation Update (if none of the other choices apply)

Screenshots (if appropriate):

Checklist

• I have read the CONTRIBUTING doc
• I have added tests that prove my fix is effective or that my feature works
• All new and existing tests passed locally
• I have added necessary documentation (if appropriate)

Further comments

If this is a relatively large or complex change, kick off the discussion by explaining why you chose the solution you did and what alternatives you considered, etc...

[diemol]

Thank you, @valfirst!