Documentation/git-log.txt: capitalize section names

This is the convention in most other files and even at the beginning of
git-log.txt

Signed-off-by: Matthieu Moy <Matthieu.Moy@imag.fr>
Reviewed-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-log.txt

@@ -84,7 +84,7 @@ include::rev-list-options.txt[]
 
 include::pretty-formats.txt[]
 
-Common diff options
+COMMON DIFF OPTIONS
 -------------------
 
 :git-log: 1
@@ -92,7 +92,7 @@ include::diff-options.txt[]
 
 include::diff-generate-patch.txt[]
 
-Examples
+EXAMPLES
 --------
 `git log --no-merges`::
 
@@ -143,12 +143,12 @@ Examples
 `git log -3`::
 	Limits the number of commits to show to 3.
 
-Discussion
+DISCUSSION
 ----------
 
 include::i18n.txt[]
 
-Configuration
+CONFIGURATION
 -------------
 
 See linkgit:git-config[1] for core variables and linkgit:git-diff[1]