Allow passing variables

[dimaMachina]

I would like to be able to pass variables with query, i made changes in repo, but every time i receive an error:

className: "bad-request"
code: 400
data: {data: null}
errors: [{message: "Unexpected GraphQL argument type "Variable"", line: 3, column: 9, path: "users"}]
message: "GraphQL processing error. (@feathers-plus/graphql)"
name: "BadRequest"
type: "FeathersError"

my service call

return app.service('api/graphql').create({
    query: `
      query($q: String) {
        users(queryBy: $q) {
          _id
          fullName
          email
          manager {
            position
          }
        }
      }
    `,
    variables: {
      q: "dmytro"
    }
  })

[eddyystop]

Am I correct in thinking that variables are still not supported after applying this PR? If this is the case, I've created #14 referencing this PR.

I'm closing this PR as I don't see its purpose. Feel free to comment if I've missed something.