Change doc.update() parameter type to Partial<T>

[markgoho]

Checklist

• Issue number for this PR: Firestore document .update() not working as intended #1245
• Docs included?: Docs exist, but don't work quite as intended
• Test units included?: no
• In a clean directory, npm install, npm run build, and npm test run successfully? (yes/no; required)

Description

Strongly typing the parameter requires that the object that's passed in is a complete match for the model. Normally though, you should be able to pass whatever you want to set and update (any number of fields in the model) and it should work.

Code sample

[markgoho]

Okay this is a shot in the dark, and I may be missing some obvious solution using Typescript, but it seems like if you take away the :T it works perfectly.

[chrste90]

What's about : Partial<T>? Does is work?

[codediodeio]

This PR would also close #1215

[markgoho]

@chris1308 Oooh, Partial<T> works!

[jamesdaniels]

Update I'm feeling but would you really want a partial for set?

[markgoho]

I don't there'd be a case where you'd want to just pass one of many properties to a .set() call. I guess part of the joy of Typescript is that we can use it to prevent ourselves from making silly mistakes, like passing a single property to a .set() call when we meant .update().

I'm going to tweak the commit and title of the PR based on your very wise question 😄