chore(deps): update rust crate gray_matter to 0.3.0

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This PR contains the following updates:

Package	Type	Update	Change
gray_matter	build-dependencies	minor	0.2.6 -> 0.3.0

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Release Notes

the-alchemists-of-arland/gray-matter-rs (gray_matter)

v0.3.2

Breaking changes

• The Matter::parse_with_struct method has been removed. Instead, you can now use the parse method with
  a struct that implements the Deserialize trait from the serde crate.
• Expose gray_matter::Error to allow engine parsing errors to be handled by the user.

Enhancements

• Implement Deserializer for Pod. No json::Value conversion is needed anymore.

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