fix: set !default for $vs-controls-deselect-text-shadow (#1468)
fix: set !default for $vs-controls-deselect-text-shadow (#1468)

- added missing `!default` for $vs-controls-deselect-text-shadow,
  which was the only one not having it
- `!default` is necessary in order to be able override the variable
sagalbot/vue-select,sagalbot/vue-select