Fix example syntax in query update method

[bmateusz]

Problem

The original example doesn't work since update requires tuples:

def update(f: (T => (Any, Any)), f2: (T => (Any, Any))*): Update[T] = NonQuotedException()

Solution

I corrected the example to use -> instead of =.

Notes

Additional notes.

Checklist

• Unit test all changes
• Update README.md if applicable
• Add [WIP] to the pull request title if it's work in progress
• Squash commits that aren't meaningful changes
• Run sbt scalariformFormat test:scalariformFormat to make sure that the source files are formatted

@getquill/maintainers

[guizmaii]

Thanks for your contribution! 🙏