Update license headers to explicitly say GPLv2+
diff --git a/TasksMeter.h b/TasksMeter.h
index 4ae6ce6..9f9ba63 100644
--- a/TasksMeter.h
+++ b/TasksMeter.h
@@ -3,7 +3,7 @@
 /*
 htop - TasksMeter.h
 (C) 2004-2011 Hisham H. Muhammad
-Released under the GNU GPLv2, see the COPYING file
+Released under the GNU GPLv2+, see the COPYING file
 in the source distribution for its full text.
 */