chore(deps): update dependency diff2html to v3.1.15

[mend-for-github-com[bot]]

This PR contains the following updates:

Package	Type	Update	Change
diff2html (source)	dependencies	patch	3.1.14 -> 3.1.15

By merging this PR, the issue #24 will be automatically resolved and closed:

Severity	CVSS Score	CVE
Medium	5.3	WS-2020-0208

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Release Notes

rtfpessoa/diff2html (diff2html)

### [`v3.1.15`](https://togithub.com/rtfpessoa/diff2html/releases/tag/3.1.15): Fix code selection [Compare Source](https://togithub.com/rtfpessoa/diff2html/compare/3.1.14...3.1.15)

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