Not converting values from css grid properties

[assuncaocharles]

Reproduction link
For reference: CSS Grid in IE: Debunking Common IE Grid Misconceptions

Current behavior

IE prefix for css grid are correctly added but with improper values:

{
    gridTemplateColumns: 'repeat(3, 1fr)' 
}

Generates:

{
    gridTemplateColumns: 'repeat(3, 1fr)', 
    msGridTemplateColumns: 'repeat(3, 1fr)',
}

Expected

It should convert values to work properly:

{
    gridTemplateColumns: 'repeat(3, 1fr)' 
}

Should generate

{
    gridTemplateColumns: 'repeat(3, 1fr)', 
    msGridTemplateColumns: '(1fr)[3]', //or '1fr 1fr 1fr'
}