doc: fix formatting in git-update-ref

Remove the parapgraph numbers from lines explaining the reflog format
and typeset these lines in monospace.

Signed-off-by: Andreas Heiduk <asheiduk@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: asheiduk

Documentation/git-update-ref.txt

@@ -129,17 +129,17 @@ a line to the log file "$GIT_DIR/logs/<ref>" (dereferencing all
 symbolic refs before creating the log name) describing the change
 in ref value.  Log lines are formatted as:
 
-    . oldsha1 SP newsha1 SP committer LF
-+
+    oldsha1 SP newsha1 SP committer LF
+
 Where "oldsha1" is the 40 character hexadecimal value previously
 stored in <ref>, "newsha1" is the 40 character hexadecimal value of
 <newvalue> and "committer" is the committer's name, email address
 and date in the standard Git committer ident format.
 
 Optionally with -m:
 
-    . oldsha1 SP newsha1 SP committer TAB message LF
-+
+    oldsha1 SP newsha1 SP committer TAB message LF
+
 Where all fields are as described above and "message" is the
 value supplied to the -m option.