`transition: var(--something, var(--fallback))` gets converted to `var(--something, false(--fallback))`

[DioEraclea]

In JSS, which uses this plugin:

example: {
  transition: 'var(--something, var(--fallback))'
}

gets converted to

.example-1-2-3 {
  transition: var(--something, false(--fallback))
}

Namely, the fallback var is being converted to false.

This issue is similar to #112

[priver]

Also

transition: box-shadow var(--animation-duration, 0.4s) var(--animation-easing, cubic-bezier(0.3, 0.3, 0.5, 1))

becomes

transition: box-shadow var(--animation-duration, 0.4s) var(--animation-easing, false(0.3, 0.3, 0.5, 1))