Update dependency gulp to ^4.0.2

Created by: renovate[bot]

This PR contains the following updates:

Package	Type	Update	New value	References	Sourcegraph
gulp (source)	devDependencies	patch	^4.0.2	homepage, source

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Release Notes

gulpjs/gulp

v4.0.2

Compare Source

Fix

• Bind src/dest/symlink to the gulp instance to support esm exports (5667666) - Ref standard-things/esm#​797

Docs

• Add notes about esm support (4091bd3) - Closes #​2278
• Fix the Negative Globs section & examples (3c66d95) - Closes #​2297
• Remove next tag from recipes (1693a11) - Closes #​2277
• Add default task wrappers to Watching Files examples to make runnable (d916276) - Closes #​2322
• Fix syntax error in lastRun API docs (ea52a92) - Closes #​2315
• Fix typo in Explaining Globs (5d81f42) - Closes #​2326

Build

• Add node 12 to Travis & Azure (b4b5a68)

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