False positive when using methods on constant userdata values in the standard library

[Amber Grace]

The following line of code emits a false positive "incorrect standard library use" warning:

local zAxis = Vector3.xAxis:Cross(Vector3.yAxis)

I was able to work around this warning by wrapping Vector3.xAxis in parentheses

    local facingVector = (Vector3.xAxis):Cross(floorCast.Normal)

[Chris Chang]

Dupe of #348.