Correct shell scripting mistake in node package generation code

tools/run_tests/build_package_node.sh

@@ -61,7 +61,7 @@ mkdir -p $output_dir
 well_known_protos=( any api compiler/plugin descriptor duration empty field_mask source_context struct timestamp type wrappers )
 
 for arch in {x86,x64}; do
-  case arch in
+  case $arch in
     x86)
       node_arch=ia32
       ;;
@@ -70,7 +70,7 @@ for arch in {x86,x64}; do
       ;;
   esac
   for plat in {windows,linux,macos}; do
-    case plat in
+    case $plat in
       windows)
         node_plat=win32
         ;;