Manually select the last argument.

This implementation does not rely on Bash-specific functionality.
diff --git a/git-flow-hotfix b/git-flow-hotfix
index 436760c..a675619 100644
--- a/git-flow-hotfix
+++ b/git-flow-hotfix
@@ -124,7 +124,7 @@
 	eval set -- "${FLAGS_ARGV}"
 
 	# read arguments into global variables
-	VERSION=${!#}
+	VERSION=$(last_arg "$@")
 	BRANCH=$PREFIX$VERSION
 }