code: function validate( opts, options ) {
  	if ( !isObject( options ) ) {
  		return new TypeError( 'invalid input argument. Options argument must be an object. Value: `' + options + '`.' );
  	}
  	opts.slug = options.slug;
  	if ( !isString( opts.slug ) ) {
  		return new TypeError( 'invalid option. `slug` option must be a primitive string. Option: `' + opts.slug + '`.' );
  	}
  	opts.file = options.file;
  	if ( !isString( opts.file ) ) {
  		return new TypeError( 'invalid option. `file` option must be a primitive string. Option: `' + opts.file + '`.' );
  	}
  	if ( options.hasOwnProperty( 'cdn' ) ) {
  		opts.cdn = options.cdn;
  		if ( !isBoolean( opts.cdn ) ) {
  			return new TypeError( 'invalid option. `cdn` option must be a primitive boolean. Option: `' + opts.cdn + '`.' );
  		}
  	}
  	return null;
  }
docs: VALIDATE // 
  FUNCTION: validate( opts, options )
  Validates function options.
  
  @param {Object} opts - destination object
  @param {Object} options - function options
  @param {String} options.slug - public Github repository slug
  @param {String} options.file - filepath
  @param {Boolean} [options.cdn] - boolean indicating whether to return a CDN URL
  @returns {Error|Null} error object or null