brew-man: only exit 1 when an error occurs

Because of "set -e" in non verbose mode brew man had an exit status
equals to 1 whereas there was no error.  The reason was that the "test"
command failed.  This patch fix this.

Closes Homebrew/homebrew#10664.

Signed-off-by: Jack Nagel <jacknagel@gmail.com>

Library/Contributions/examples/brew-man

@@ -45,7 +45,7 @@ do
   ronn --roff --pipe --organization='Homebrew' --manual='brew' $i > $target_file
 done
 
-test "$1" = '--verbose' || \
-test "$1" = '-v' && {
+if test "$1" = '--verbose' || test "$1" = '-v'
+then
   man brew
-}
+fi