Prevent prototype pollution while parsing query strings on V1

[Hunter-Dolan]

Description

This PR ports the changes made in #2494 for Mithril 2.x and above to Mithril 1.1.x.

Motivation and Context

• It fixes a vulnerability in the query string parser that led to direct prototype pollution (https://npmjs.com/advisories/1094).

• It resolves Fix high severity parseQueryString vulnerability in v1.1 too #2519

How Has This Been Tested?

• It implements the same tests used in Prevent prototype pollution while parsing query strings #2494
• In addition, tests were run using npm run test and they passed in the following env:
  • Mac OS X 10.14.5
  • NodeJS v10.15.0

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)
• Documentation 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.
• I have updated docs/change-log.md

[dead-claudia]

Could you make that one tweak to the changelog? That's my only nit.

[Hunter-Dolan]

@isiahmeadows Great! All set on that, let me know if if there is anything else.

[dead-claudia]

Sorry for the delay! Been a bit packed with stuff lately.

[dead-claudia]

Heads up, this change has been released in v1.1.7 alongside a small IE fix, but I'm still working on catching up the docs, putting together a quick announcement, and notifying npm to change their advisory.