fix(TypeScript): express() is an express Application in strinct

[nigrosimone]

The type returned by express() is not assignable to an express Application in strict, so code typed against Express does not compile with it, for example:

import express, { Application } from "ultimate-express";
const app: Application = express()

raise error:

error TS2322: Type 'UltimateExpress' is not assignable to type 'Application'.