git-log.txt: fix typesetting of example "git-log -L" invocation

All surrounding examples are typeset as monospaced text. Follow suit.

Signed-off-by: Eric Sunshine <sunshine@sunshineco.com>
Acked-by: Thomas Rast <trast@inf.ethz.ch>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-log.txt

@@ -153,7 +153,7 @@ Examples
 	This makes sense only when following a strict policy of merging all
 	topic branches when staying on a single integration branch.
 
-git log -L '/int main/',/^}/:main.c::
+`git log -L '/int main/',/^}/:main.c`::
 
 	Shows how the function `main()` in the file 'main.c' evolved
 	over time.