fix(Node): Fix error and crash due to custom cacheFolder in achecker.yml

[sct-will]

Code to address the case when a user configures a custom cacheFolder in achecker.yml.

The problem was, the previous code did not account for the fact that the code runs in the accessibility_checker/src/lib folder, so a require( ) has to be relative to this directory, hence the need to go up two directory levels if the cacheFolder is relative path and not a fully qualified path.

This update works for any cacheFolder directory.

• Automated tool bug

This PR is related to the following issue(s):

#1149

Additional information can be found here:

Testing reference:

In order to test, edit cacheFolder in achecker.yml (as shown in the lines below) to any desired directory, then run automated test to verify there are no failures.

# optional - Where the tool can read/write cached files (ace-node.js / archive.json)
# cacheFolder: /tmp/accessibility-checker
cacheFolder: accessibility-checker

I have conducted the following for this PR:

• I validated this code in Chrome and FF
• I validated this fix in my local env
• I provided details for testing
• This PR has been reviewed and is ready for test
• I understand that the title of this PR will be used for the next release notes.