Safari doesn't render transparent gradients well

[chrisgarrity]

Expected Behavior

Please describe what should happen
This project https://preview.scratch.mit.edu/#222183421 should look like:

Actual Behavior

Describe what actually happens
On Safari:

Steps to Reproduce

Explain what someone needs to do in order to see what's described in Actual behavior above
View https://preview.scratch.mit.edu/#222183421

Operating System and Browser

e.g. Mac OS 10.13.5 Safari 11.1.1

[kyleplo]

Probably related to scratchfoundation/scratch-render#313

[thisandagain]

Moved to scratchfoundation/scratch-render#315