Fix types minor errors

[H-L]

Hello,

First of all thanks for your hard work on the v3.0.0 !

I recently updated the deps in a project I work on, and tsc prompted some minor TS errors from Strophe.

So here is a quick PR to fix the errors encountered :

• In connection.js and connection.d.ts, at the addHandler method, the id parameter should be optional since it is already optional in Handler.constructor
• In index.d.ts, Strophe and Connection were added to the export, for simplicity purposes

Let me know if you need any changes on the PR.

Best regards !

[H-L]

Hello !
The changes requested have been applied.

The changes on the .d.ts files are what is returned by the make dist/types command, nothing else. Let me know if you need anything else.

Best regards and have a great summer 🏖️

[jcbrand]

Thanks!