Fix lint errors

[paulshryock]

Fix the following lint errors:

gulpfile.js
line 31:5   'gulpWatch' is assigned a value but never used.
✖ 1 errors  ⚠ 0 warnings

src/server/admin/js/index.js
line 32:10  'renderDashboard' is defined but never used.
✖ 1 errors  ⚠ 0 warnings

Standard linter results
======================================
✖ Errors total: 1
⚠ Warnings total: 0

src/client/_assets/js/modules/pledges-and-certificates.js
line 82:12  'createElement' is defined but never used.
line 131:12 'addDomMarkup' is defined but never used.
✖ 2 error   ⚠ 0 warning

src/client/_assets/js/modules/send-certificate.js
line 79:7   'headerImage' is assigned a value but never used.
✖ 1 errors  ⚠ 0 warnings

Standard linter results
======================================
✖ Errors total: 4
⚠ Warnings total: 0

To Reproduce

1. Run npm run build:client
2. See errors in console output