org: really hide the plantuml logo

Fix a5d6aa25.

* doc/org/.dir-locals.el.in, doc/org/init.el.in: Use
-Djava.awt.headless=true, not -Djava.awt.headless.

doc/org/.dir-locals.el.in

@@ -41,7 +41,7 @@
                   ; Prevent the plantuml logo to annoying appear on
                   ; top of whatever you are doing when the project
                   ; compiles in the background.
-                  (:java . "-Djava.awt.headless")))
+                  (:java . "-Djava.awt.headless=true")))
 	      (org-publish-project-alist
 	       . (("spot-html"
 		   :base-directory "."

doc/org/init.el.in

@@ -37,7 +37,7 @@
         ;; prevent the plantuml logo to annoying appear on top of
         ;; whatever you are doing when the project compiles in the
         ;; background.
-        (:java . "-Djava.awt.headless")))
+        (:java . "-Djava.awt.headless=true")))
 
 (setenv "PATH"
 	(concat "@abs_top_builddir@/bin" path-separator (getenv "PATH")))