[vala] manual: Add language="vala" attribute to Devhelp version

[Rico Tzschichholz <ricotz src gnome org>]

commit 95ea421a7007964a87fc5d4d9573096aa7c64357
Author: Alistair Thomas <astavale yahoo co uk>
Date:   Sun Mar 12 19:29:48 2017 +0000

    manual: Add language="vala" attribute to Devhelp version

 doc/manual/devhelp.xsl |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/doc/manual/devhelp.xsl b/doc/manual/devhelp.xsl
index 3a1db14..92036c3 100644
--- a/doc/manual/devhelp.xsl
+++ b/doc/manual/devhelp.xsl
@@ -13,7 +13,7 @@
   />
 
   <xsl:template match="/">
-    <book title="{/article/section/title/text()}" link="index.html" author="" name="vala" version="2">
+    <book title="{/article/section/title/text()}" link="index.html" author="" name="vala" language="vala" 
version="2">
       <chapters>
         <xsl:apply-templates select="/article/section/section"/>
       </chapters>