metalsmith-pagination.js
function interpolate (path, data) {
  return path.replace(/:(\w+)/g, function (match, param) {
    return data[param]
  })
}
function interpolate (path, data) {
  return path.replace(/:(\w+)/g, function (match, param) {
    return data[param]
  })
}
Interpolate the page path with pagination variables.

@param  {String} path
@param  {Object} data
@return {String}