Update version to 18.2.0-rc6

Signed-off-by: Andres Gomez <agomez@igalia.com>
diff --git a/VERSION b/VERSION
index d35df96..a9045f6 100644
--- a/VERSION
+++ b/VERSION
@@ -1 +1 @@
-18.2.0-rc5
+18.2.0-rc6