Update CHANGELOG for v1.0.3

***NO_CI***

Author: nfbot

CHANGELOG.md

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+# Changelog
+
+## [**Changes available only in 'Preview' NuGet packages:**](https://github.com/nanoframework/System.Device.I2c.Slave/tree/HEAD)
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+[Full Changelog](https://github.com/nanoframework/System.Device.I2c.Slave/compare/0f56da3690116539cfe3aa98742442534ce0f702...HEAD)
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+**Documentation and other chores:**
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+- Update Intellisense comment [\#1](https://github.com/nanoframework/System.Device.I2c.Slave/pull/1)
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+
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+\* *This Changelog was automatically generated by [github_changelog_generator](https://github.com/github-changelog-generator/github-changelog-generator)*