classCallCheck (instance, ctor) {
    if (!(instance instanceof ctor)) {
      throw utils.err(`${ctor.name}`)(500, 'Cannot call a class as a function')
    }
  }
Verified that the given constructor is being invoked via `new`, as opposed
to just being called like a normal function.

@example
import { utils } from 'js-data';
function Cat () {
  utils.classCallCheck(this, Cat);
}
const cat = new Cat(); // this is ok
Cat(); // this throws an error

@method utils.classCallCheck
@param {*} instance Instance that is being constructed.
@param {Constructor} ctor Constructor function used to construct the
instance.
@since 3.0.0
@throws {Error} Throws an error if the constructor is being improperly
invoked.