update playground highlighting

[tsnobip]

Module types and record optional field punning was not well supported, this is now fixed with rescript-lezer v0.7.0, eg:

module Foo: {
  type t
  let make: (~bar: option<int>=?, ~baz: option<int>=?) => t
} = {
  type t = {
    bar?: option<int>,
    baz?: option<int>,
  }
  let make = (~bar: option<option<int>>=?, ~baz=?) => {?bar, ?baz}
}

compare highlighting of this code with this PR vs master

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