Fix type of filter

[sandersn]

The source of filter is

  filter (paths) {
    return make_array(paths).filter(path => this._filter(path))
  }

So I think it is pretty obvious that filter's type is string[] => string[].

Also remove redundant types from filter's JSDoc in index.d.ts.

[kaelzhang]

Thanks! Landed in 3.3.8