Enable cds watch hello

by moving the `hello` implementation into the subfolder `srv`

hello/srv/world.cds

@@ -0,0 +1,3 @@
+service say {
+  function hello (to:String) returns String;
+}

hello/srv/world.js

@@ -0,0 +1,3 @@
+module.exports = class say {
+  hello(req) { return `Hello ${req.data.to}!` }
+}

hello/srv/world.ts

@@ -0,0 +1,5 @@
+module.exports = class say {
+    hello(req: any) {
+        return `Hello ${req.data.to} from a TypeScript file!`
+    }
+}