add sourceMappingUrl to output in node module

If options.outSourceMap is specified the sourceMappingURL comment
should be appended to the output stream

tools/node.js

@@ -126,6 +126,11 @@ exports.minify = function(files, options) {
     }
     var stream = UglifyJS.OutputStream(output);
     toplevel.print(stream);
+
+    if(options.outSourceMap){
+        stream += "\n//# sourceMappingURL=" + options.outSourceMap;
+    }
+
     return {
         code : stream + "",
         map  : output.source_map + ""