[Bug]: `vinyl-sourcemaps-apply` should not be in dev deps (for gulp-purgecss)

[j0k3r]

Describe the bug

While upgrading from 4.1.3 to 5.0.0, we got an error during the process:

$ gulp
[11:06:05] Requiring external module ts-node/register
Error: Cannot find module 'vinyl-sourcemaps-apply'
Require stack:
- /home/travis/build/20minutes/hela/node_modules/gulp-purgecss/lib/gulp-purgecss.js
- /home/travis/build/20minutes/hela/scripts/buildCssPageType.ts
- /home/travis/build/20minutes/hela/gulpfile.ts

That new deps used in index.ts might move to direct deps instead of dev deps:

To Reproduce

I guess just upgrading an existing project using gulp-purgecss from v4 to v5

Expected Behavior

No error throw about the missing package.

Environment

• MacOS but the problem appear on Travis too.
• Node 16

Add any other context about the problem here

No response

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