consolidate Gulp build

- move task require to gulpfile.js/tasks/index.js
- abbreviate variable names
- use ospath where appropriate
4 jobs for master in 1 minute and 39 seconds
Status Job ID Name Coverage
  Setup
passed #139971241
yarn

00:01:01

 
  Verify
failed #139971242
lint

00:00:37

 
  Deploy
skipped #139971243
bundle-stable
skipped #139971244
pages
 
Name Stage Failure
failed
lint Verify
    at Module.require (internal/modules/cjs/loader.js:637:17)
at require (internal/modules/cjs/helpers.js:22:18)
at Object.<anonymous> (/builds/antora/antora-ui-default/gulpfile.js/index.js:14:86)
at Module._compile (internal/modules/cjs/loader.js:689:30)
at Object.Module._extensions..js (internal/modules/cjs/loader.js:700:10)
at Module.load (internal/modules/cjs/loader.js:599:32)
at tryModuleLoad (internal/modules/cjs/loader.js:538:12)
at Function.Module._load (internal/modules/cjs/loader.js:530:3)
ERROR: Job failed: exit code 1