revisions.txt: change "rev" to "<rev>"

In revisions.txt, there were some instances of a rev argument being
written as "rev". However, since they didn't mean the string literal,
write "<rev>", instead.

Signed-off-by: Denton Liu <liu.denton@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/revisions.txt

diff --git a/Documentation/revisions.txt b/Documentation/revisions.txt
index 7d1bd44..2859d77 100644
--- a/Documentation/revisions.txt
+++ b/Documentation/revisions.txt
@@ -159,12 +159,12 @@
   '<rev>{caret}0'
   is a short-hand for '<rev>{caret}\{commit\}'.
 +
-'rev{caret}\{object\}' can be used to make sure 'rev' names an
-object that exists, without requiring 'rev' to be a tag, and
-without dereferencing 'rev'; because a tag is already an object,
+'<rev>{caret}\{object\}' can be used to make sure '<rev>' names an
+object that exists, without requiring '<rev>' to be a tag, and
+without dereferencing '<rev>'; because a tag is already an object,
 it does not have to be dereferenced even once to get to an object.
 +
-'rev{caret}\{tag\}' can be used to ensure that 'rev' identifies an
+'<rev>{caret}\{tag\}' can be used to ensure that '<rev>' identifies an
 existing tag object.
 
 '<rev>{caret}{}', e.g. 'v0.99.8{caret}{}'::