Update constraints.md (flutter#10070)

Updated the values of constraints for Widget.

_Description of what this PR is changing or adding, and why:_

_Issues fixed by this PR (if any):_

## Presubmit checklist

- [x] This PR doesn’t contain automatically generated corrections
(Grammarly or similar).
- [x] This PR follows the [Google Developer Documentation Style
Guidelines](https://developers.google.com/style) — for example, it
doesn’t use _i.e._ or _e.g._, and it avoids _I_ and _we_ (first person).
- [x] This PR uses [semantic line
breaks](https://github.com/dart-lang/site-shared/blob/main/doc/writing-for-dart-and-flutter-websites.md#semantic-line-breaks)
of 80 characters or fewer.

Co-authored-by: Brett Morgan <[email protected]>

src/ui/layout/constraints.md

@@ -69,8 +69,8 @@ The negotiation goes something like this:
 
 **Widget**: "Hey parent, what are my constraints?"
 
-**Parent**: "You must be from `80` to `300` pixels wide,
-   and `30` to `85` tall."
+**Parent**: "You must be from `0` to `300` pixels wide,
+   and `0` to `85` tall."
 
 **Widget**: "Hmmm, since I want to have `5` pixels of padding,
    then my children can have at most `290` pixels of width