Update cheat-sheet.mdx

[asavchuk]

Describe the changes proposed in this Pull Request.

If the PR fixes a specific issue, reference the issue with Fixes #.

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Pull Request Checklist

• [ ] If the changes are being made to code, ensure the version in pubspec.yaml is updated.
• [ ] Increment the major/minor/patch/patch-count, depending on the complexity of change
• [ ] Add the necessary unit tests to ensure the coverage does not drop
• [ ] Update the Changelog to include all changes made in this PR, organized by version
• [ ] Run the melo run set_version command from the root directory
• [ ] Include the necessary reviewers for the PR
• [ ] Update the docs if there are any API changes or additions to functionality

[netlify[bot]]

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[codecov[bot]]

Codecov Report

Merging #878 (b849783) into master (87ba7d1) will increase coverage by 1.43%. The diff coverage is n/a.

@@             Coverage Diff             @@
##           master      #878      +/-   ##
===========================================
+ Coverage   98.56%   100.00%   +1.43%     
===========================================
  Files          37         5      -32     
  Lines        1460        97    -1363     
===========================================
- Hits         1439        97    -1342     
+ Misses         21         0      -21     

Flag	Coverage Δ
flutter_mobx	100.00% <ø> (ø)
mobx	?

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
mobx/lib/src/core/action.dart
mobx/lib/src/core/reaction_helper.dart
mobx/lib/src/core/observable.dart
mobx/lib/src/core.dart
mobx/lib/src/core/atom.dart
...b/src/api/extensions/observable_map_extension.dart
...rc/api/extensions/observable_stream_extension.dart
...src/api/extensions/primitive_types_extensions.dart
mobx/lib/src/core/spy.dart
mobx/lib/src/listenable.dart
... and 22 more

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