Fix for Styleguidekit v4

Author: EvanLovely

src/PatternLab/Config.php

@@ -242,6 +242,7 @@ public static function init($baseDir = "", $verbose = true) {
 		self::setExposedOption("cacheBuster");
 		self::setExposedOption("defaultPattern");
 		self::setExposedOption("defaultShowPatternInfo");
+		self::setExposedOption("patternExtension");
 		self::setExposedOption("ishFontSize");
 		self::setExposedOption("ishMaximum");
 		self::setExposedOption("ishMinimum");