lib/by.js
function byClass (c) {
  c = classnames(c)
  if (/^\./.test(c)) {
    throw new Error('No need to "." on start')
  }
  return bySelector(`.${c}`)
}
function byClass (c) {
  c = classnames(c)
  if (/^\./.test(c)) {
    throw new Error('No need to "." on start')
  }
  return bySelector(`.${c}`)
}
By class name
@param {string} c - Class name
@returns {string} Selector by class