Update setup-node-mavericks.bash

setup-node-mavericks.bash

@@ -8,7 +8,7 @@ if [ -z "${PREFIX-}" ]; then
   PREFIX=""
 fi
 
-if [ -z "$NODE_PATH" ]; then
+if [ -n "$NODE_PATH" ]; then
   node_install_path=$(dirname $(dirname $NODE_PATH))
 else
   node_install_path=$PREFIX/usr/local