Fix typings path

The typings file name is wrongly pointing to `./lib/index.ts` (which does not exists) creating a tsc compilation error

```error TS7016: Could not find a declaration file for module '@tsed/swagger'. '/Users/javiergomez/workspace/node/tsed/test/node_modules/@tsed/swagger/lib/index.js' implicitly has an 'any' type.
  Try `npm install @types/tsed__swagger` if it exists or add a new declaration (.d.ts) file containing `declare module '@tsed/swagger';`

3 import {Description, Example} from "@tsed/swagger";```

packages/swagger/package.json

@@ -3,7 +3,7 @@
   "version": "5.60.6",
   "description": "Swagger package for Ts.ED framework",
   "main": "./lib/index.js",
-  "typings": "./lib/index.ts",
+  "typings": "./lib/index.d.ts",
   "scripts": {
     "build": "tsc --build tsconfig.compile.json",
     "build:doc": "tsc --build tsconfig.doc.json"
@@ -20,4 +20,4 @@
   "devDependencies": {
     "@tsed/common": "5.60.6"
   }
-}
+}