Changed proxyContextEs5 name to proxylessContext, fixed addRuleSet bug

[ev-akarel]

Description

Fixed addRuleSet method so that it returns the context object correctly.

Fixes bug in PR #171 which fixes issue #45.

Type of change

• 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 not work as expected)
• Other (please, feel free to specify what kind of change it is)

Checklist:

• I have created my branch from a recent version of master
• The code is clean and easy to understand
• I have written tests to guarantee that everything is working properly
  • I have, but out of scope for this project, since they needed to be in an environment without a Proxy object.
• I have made corresponding changes to the documentation
• I have added changes to the Unreleased section of the CHANGELOG

[ev-akarel]

@NoemiRozpara This is to address the issue discussed in your v8n PR #171. The addRuleSet method was just not returning anything, which was causing the error. I also updated the changelog and docs, so your PR should be good to go once this gets merged in. Let me know if you have any questions.

[taiga533]

@ev-akarel
Hi.
I think this pull request should be reworked into a pull request from your repository to imbrn/v8n.