[libgda] Doc. correction

[Vivien Malerba <vivien src gnome org>]

commit 0d82daea201b4ac5b4da29293aa6fb56527d0ec0
Author: Vivien Malerba <malerba gnome-db org>
Date:   Tue May 20 21:32:12 2014 +0200

    Doc. correction

 doc/C/prov-writing-virtual-methods.xml |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/doc/C/prov-writing-virtual-methods.xml b/doc/C/prov-writing-virtual-methods.xml
index 544d59e..ac1af71 100644
--- a/doc/C/prov-writing-virtual-methods.xml
+++ b/doc/C/prov-writing-virtual-methods.xml
@@ -68,7 +68,7 @@
     </para>
 
     <sect2 id="prov-create-worker">
-      <title>create_worker() - optional</title>
+      <title>create_worker() - mandatory</title>
       <para>
        Regarding thread safety, each database API has one of the following behaviours:
        <orderedlist>