function msg(method, what, type) {
  return 'micromatch.' + method + '(): ' + what + ' should be ' + type + '.';
}
Make error messages consistent. Follows this format:

```js
msg(methodName, argNumber, nativeType);
// example:
msg('matchKeys', 'first', 'an object');
```

@param  {String} `method`
@param  {String} `num`
@param  {String} `type`
@return {String}