Make "gap" automatically use "grid-gap" on Safari

[w3bdesign]

There is an issue where gap- is not supported on older Safari devices.

As a result, there is a need to use grid-gap: x px with CSS in order to get it to work.

I suggest that this gets fixed in one way or another so that there is no need for a manual CSS fix.

[adamwathan]

Hey! We used to include grid-gap in Tailwind v1.x but we don't support old Safari anymore as of Tailwind v2.0. The regular gap property works as of Safari 12 on both macOS and iOS.