change ref docs url format from 1_5 to v1.5

docs/api-reference/v1.5/server.js

@@ -0,0 +1,7 @@
+var static = require('node-static');
+var file = new static.Server();
+require('http').createServer(function(request, response) {
+  request.addListener('end', function() {
+    file.serve(request, response);
+  }).resume();
+}).listen(process.env.PORT || 3000);