git-config: update doc for --get with multiple values

Since commit 00b347d3 (git-config: do not complain about duplicate
entries, 2012-10-23), "git config --get" does not exit with an error if
there are multiple values for the specified key but instead returns the
last value.  Update the documentation to reflect this.
Signed-off-by: NJohn Keeping <john@keeping.me.uk>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Documentation/git-config.txt

@@ -82,7 +82,7 @@ OPTIONS
 --get::
 	Get the value for a given key (optionally filtered by a regex
 	matching the value). Returns error code 1 if the key was not
-	found and error code 2 if multiple key values were found.
+	found and the last value if multiple key values were found.
 
 --get-all::
 	Like get, but does not fail if the number of values for the key