signature: Defining KeyLocator as an optional field in generic SignatureInfo

Change-Id: I2e2850bdf5b1795c07aea208fe8c80c8b6df509f
diff --git a/conf.py b/conf.py
index e0de7f2..ee871a0 100644
--- a/conf.py
+++ b/conf.py
@@ -186,7 +186,7 @@
 # (source start file, target name, title, author, documentclass [howto/manual]).
 latex_documents = [
   ('index', 'ndn-spec.tex', u'NDN specification Documentation',
-   u'NDN Project Team', 'manual'),
+   u'NDN Project Team', 'howto'),
 ]
 
 # The name of an image file (relative to this directory) to place at the top of