Add file definition to package.json

[Romakita]

{
"name": "ts-express-decorators",
"version": "1.2.0-0",
"description": "Use TypeScript decorators to create your Express application and Rest API",
"main": "index.js",
"typings": "index.d.ts"
...
}
Need a new task to generate the index.d.ts.