Update haxe.hxproj (#5398)

This is useful to find types only in std

haxe.hxproj

@@ -15,7 +15,7 @@
   </output>
   <!-- Other classes to be compiled into your SWF -->
   <classpaths>
-    <!-- example: <class path="..." /> -->
+    <class path="std" />
   </classpaths>
   <!-- Build options -->
   <build>
@@ -320,4 +320,4 @@
   </options>
   <!-- Plugin storage -->
   <storage />
-</project>
+</project>