mark gen as Generated root

Author: gregsh

grammar-kit.iml

@@ -4,7 +4,7 @@
   <component name="NewModuleRootManager" inherit-compiler-output="true">
     <exclude-output />
     <content url="file://$MODULE_DIR$">
-      <sourceFolder url="file://$MODULE_DIR$/gen" isTestSource="false" />
+      <sourceFolder url="file://$MODULE_DIR$/gen" isTestSource="false" generated="true" />
       <sourceFolder url="file://$MODULE_DIR$/support" isTestSource="false" />
       <sourceFolder url="file://$MODULE_DIR$/tests" isTestSource="true" />
     </content>