(GH-156) cChocoSource can now update source URL

[bozho]

Description

cChocoSource can now update source URL on an existing source.

Related Issue

Fixes #156

How Has This Been Tested?

Running a test DSC configuration will update source URL on an existing Chocolatey source.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

[pauby]

I've tested these changes and can confirm they work! Thanks @bozho for your contribution!