function onRead( error, file ) {
		if ( error ) {
			return done( error );
		}
		file = file.toString();
		if ( opts.encoding === 'utf8' ) {
			file = removeBOM( file );
		}
		if ( opts.reviver ) {
			file = parseJSON( file, opts.reviver );
		} else {
			file = parseJSON( file );
		}
		if ( instanceOf( file, Error ) ) {
			return done( file );
		}
		done( null, file );
	}
Callback invoked upon reading a file.

@private
@param {(Error|null)} error - error object
@param {(Buffer|string)} file - file contents
@returns {void}