fix(CDVWebViewEngine): use NSURL absoluteString value for stringWithFormat

[erisu]

Motivation and Context

Description

Use NSURL absolute string value when used with stringWithFormat.

Testing

• npm t
• Standard Cordova Project Build Test

Does not cover embedded

Checklist

• I've run the tests to see all new and existing tests pass
• I added automated test coverage as appropriate for this change
• Commit is prefixed with (platform) if this change only applies to one platform (e.g. (android))
• If this Pull Request resolves an issue, I linked to the issue in the text above (and used the correct keyword to close issues using keywords)
• I've updated the documentation if necessary

[codecov-commenter]

Codecov Report

Merging #1353 (a0b29c9) into master (6db1b6e) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1353   +/-   ##
=======================================
  Coverage   78.62%   78.62%           
=======================================
  Files          15       15           
  Lines        1773     1773           
=======================================
  Hits         1394     1394           
  Misses        379      379           

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