Escape Git's exec path in contrib/rerere-train.sh script

Whitespace can cause the source command to fail. This is usually not a
problem on Unix systems, but on Windows Git is likely to be installed
under "C:/Program Files/", thus rendering the script broken.

Signed-off-by: Daniel Knittl-Frank <knittl89+git@googlemail.com>
Signed-off-by: Jeff King <peff@peff.net>

contrib/rerere-train.sh

@@ -7,7 +7,7 @@ USAGE="$me rev-list-args"
 
 SUBDIRECTORY_OK=Yes
 OPTIONS_SPEC=
-. $(git --exec-path)/git-sh-setup
+. "$(git --exec-path)/git-sh-setup"
 require_work_tree
 cd_to_toplevel