Improve getDefaultProvider types

[nelkor]

I'm using ethers + typescript and I'm forced to call the provider this way:

const provider = ethers.getDefaultProvider(null as unknown as string)

The problem is that getDefaultProvider types require passing a first argument, although in fact it is optional. As a result, I have to cheat with typescript just to run the code. I add just one character to the codebase and the first argument becomes optional, which it really is. This seems to improve the development experience, take a look at the new code:

const provider = ethers.getDefaultProvider()

[ricmoo]

Merged into v6.11.0.

Thanks! :)