Update setup-node-ubuntu.bash

setup-node-ubuntu.bash

@@ -8,10 +8,10 @@ if [ -z "${PREFIX-}" ]; then
   PREFIX=""
 fi
 
-if [ -n "$NODE_PATH" ]; then
-  node_install_path=$(dirname $(dirname $NODE_PATH))
-else
+if [ -z "${NODE_PATH-}" ]; then
   node_install_path=$PREFIX/usr/local
+else
+  node_install_path=$(dirname $(dirname $NODE_PATH))
 fi
 
 NODEJS_VER=${1}