Update bindgen requirement from 0.54 to 0.56

[dependabot-preview]

Updates the requirements on bindgen to permit the latest version.

Changelog

Sourced from bindgen's changelog.

0.56.0

Released 2020/11/26

Added

• Objective-c bindings generate From<ChildClass> for ParentClass as well as TryFrom<ParentClass> for ChildClass (#1883[]).
• Experimental dynamic library support via dynamic_library_name (#1846).
• Option to disable deriving Default on a per-struct basis (#1930).

Changed

• Objective-c bindings borrow self rather than take ownership (#1883[]).
• Templates and enums now correctly use the same naming scheme as other types (#1891).

Fixed

• Constructors in wasm32 now return a value. (#1877).
• Fixed objective-c protocol impl blocks for parent classes's protocols (#1883[]).

#1883: rust-lang/rust-bindgen#1883

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0.55.1

Released 2020/08/24.

Fixed

• Fixed a regression where anonymous enums referenced by members or such won't generate valid Rust code. (#1882).

---

0.55.0

Released 2020/08/23.

Removed

• Support for libclang 3.8 has been removed (#1830).

Added

• Added options to avoid deriving the Debug trait (#1858).

• Added options to allow to override the default anonymous field prefix (#1859).

Commits

• 11ae350 v0.56.0
• d808261 Add --no-default <regex> flag
• 30fb4ec Remove cfg-if dependency.
• 01cbe44 dyngen: Handle variadic functions.
• 7792d63 codegen: Minor nits for dynamic function generation.
• c2b5c46 Add tests for dynamic binding generation
• fc5fa9a Add dynamic loading support
• db3d170 tests: Added option to hand check test differences.
• 2c72903 Rustfmt to green up CI.
• 90b801f Update clang-sys dependency
• Additional commits viewable in compare view

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[dependabot-preview]

Superseded by #58.