vis-open: Use basename of $0 in usage message

If vis-open is placed in a user's PATH and executed then $0 will be
vis-open's absolute path:

  $ vis-open -h
  usage: /usr/local/bin/vis-open [-h] [-p prompt] [file-pattern]

This isn't very pretty, so use basename(1) on $0:

  $ vis-open -h
  usage: vis-open [-h] [-p prompt] [file-pattern]

1 files changed, 1 insertions, 1 deletions

diff --git a/vis-open b/vis-open
index a47249f..b170f0c 100755
--- a/vis-open
+++ b/vis-open
@@ -7,7 +7,7 @@ PATTERN="."
 while [ $# -gt 0 ]; do
 	case "$1" in
 		-h|--help)
-		echo "usage: $0 [-h] [-p prompt] [file-pattern]"
+		echo "usage: $(basename $0) [-h] [-p prompt] [file-pattern]"
 		exit 0;
 		;;
 		-p)