Bump gulp-sourcemaps from 1.12.1 to 3.0.0

[dependabot[bot]]

Bumps gulp-sourcemaps from 1.12.1 to 3.0.0.

Release notes

Sourced from gulp-sourcemaps's releases.

Security Fixes

Nothing changed to the overall API.

However the following security fixes lead to the following:

• acorn which caused us to drop support for Node < 6 gulp-sourcemaps/gulp-sourcemaps#376
• css bump #380

Commits

• 2bcfcbb 3.0.0
• d8bed0c Merge pull request #373 from adrian3d/update/doc-gulp-4
• 5686db3 Merge pull request #380 from kennyr87/gh-378/upgrade-css
• 2c66b2c Depdenency: Upgrade css to v3.0.0
• 9a9289b Breaking: Drop Node <6 support & upgrade identity-map which uses changes CSS ...
• 11d1e31 Update doc to gulp 4
• bd0aeb0 Docs: Temporarily point at phated/gulp-sourcemaps for AppVeyor badge
• 7e69e97 Build: Ensure tests pass on Windows
• 404eb5b Docs: Update badges
• 8a22ecc Scaffold: Convert repository to use gulp patterns (closes #357) (#367)
• Additional commits viewable in compare view

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