Adds CSS Grid properties to list of unitless numbers

[ericsakmar]

Adds the following CSS Grid properties to the list of unitless numbers:

• gridColumnStart
• gridColumnEnd
• gridColumnSpan (ie/ms only)
• gridRowStart
• gridRowEnd
• gridRowSpan (ie/ms only)

Without these values in the list, the code appends a px, which is not valid for these properties.

[gaearon]

Is this list exhaustive?

[ericsakmar]

It's exhaustive to the CSS grid spec, but not necessarily exhaustive to other newer unitless properties outside of that spec.

[flarnie]

Initially my questions were:

1. Is it too soon to add CSS Grid syntax to React? What if the spec changes?
2. Does this miss any other CSS Grid properties?

Clearly though if we already support gridColumn and gridRow then we should support the more specific grid properties too. And it looks like this does not miss any other non-px grid properties.

Thanks for submitting this @ericsakmar!