Upgrade diff to 4.0.1

[akshayas]

PR checklist

• Addresses an existing issue: fixes #0000
• New feature, bugfix, or enhancement
  • Includes tests
• Documentation update

Overview of change:

Github/dependabot reported a high severity bug with jsdiff. The exact wording is

WS-2018-0590 More information
high severity
Vulnerable versions: < 3.5.0
Patched version: 3.5.0
A vulnerability was found in diff before v3.5.0, the affected versions of this package are vulnerable to Regular Expression Denial of Service (ReDoS) attacks.

This diff bumps up the version to the latest available jsdiff 4.0.1.

Is there anything you'd like reviewers to focus on?

No

CHANGELOG.md entry:

N/A

[palantirtech]

Thanks for your interest in palantir/tslint, @akshayas! Before we can accept your pull request, you need to sign our contributor license agreement - just visit https://cla.palantir.com/ and follow the instructions. Once you sign, I'll automatically update this pull request.

[adidahiya]

thanks @akshayas