Add touch command after unpacking our ext js files.

Files inside a zip archive have an older modified date than
the zip which contains them.
Touching the files after their creation will prevent unnecessary
execution of the target and will speed up the build.
Signed-off-by: Emmanuel Kasper <e.kasper@proxmox.com>

www/ext4/Makefile

@@ -12,6 +12,7 @@ ${EXTDATA}: ${EXTJSSRC}
 	rm -rf ${EXTJSDIR} extjs
 	unzip -x ${EXTJSSRC}
 	mv ${EXTJSDIR} extjs
+	touch ${EXTDATA}
 
 all: ${EXTDATA}