Fix issue with ES Express import

[adamjmcgrath]

Description

Use import = require() syntax to import a CommonJS style export = type from @types/express

References

fixes #309
https://github.com/DefinitelyTyped/DefinitelyTyped/blob/master/types/express/index.d.ts
https://www.typescriptlang.org/docs/handbook/modules.html#export--and-import--require

Testing

I'd like to remove the esModuleInterop flag from https://github.com/auth0/node-jwks-rsa/blob/master/tsconfig.json#L16 so our CI tests would verify this, but I can't because out express-jwt dependencies require this. So tested manually with basic TS config.

Checklist

• I have added documentation for new/changed functionality in this PR or in auth0.com/docs
• All active GitHub checks for tests, formatting, and security are passing
• The correct base branch is being used, if not master

[rbutera]

lets get this merged, latest release is breaking all of our nodejs auth0 apps