Fix gradient control

[richtabor]

The gradient control within Gutenberg requires rgb formatting, instead of hsl. This PR resolves that.

Before:

After:

[cypress]

---

Test summary

6 • 8 • 0 • 0

---

Run details

Project	Go
Status	Failed
Commit	92d97dd
Started	Jun 8, 2020 5:13 PM
Ended	Jun 8, 2020 5:14 PM
Duration	00:43 💡
OS	Linux Debian - 10.4
Browser	Firefox 77

View run in Cypress Dashboard ➡️

---

Failures

	barista-welcoming.spec.js ⏯		1
1	VR Testing: barista - welcoming > Loads additional pages
	barista-traditional.spec.js ⏯		1
1	VR Testing: barista - traditional > Loads additional pages
	bento-welcoming.spec.js ⏯		1
1	VR Testing: bento - welcoming > Loads additional pages
	miller-welcoming.spec.js ⏯		1
1	VR Testing: miller - welcoming > Loads additional pages
	miller-traditional.spec.js ⏯		1
1	VR Testing: miller - traditional > Loads additional pages
	barista-modern.spec.js ⏯		1
1	VR Testing: barista - modern > Loads additional pages
	bento-modern.spec.js ⏯		2
1	VR Testing: bento - modern > Loads frontpage
2	VR Testing: bento - modern > Loads additional pages

---

This comment has been generated by cypress-bot as a result of this project's GitHub integration settings. You can manage this integration in this project's settings in the Cypress Dashboard

[EvanHerman]

@richtabor Looks good to me - we just need to fix the unit tests and figure out why those visual regression tests are failing. They might fast fail because the unit tests are failing first.