Update bindgen requirement from 0.50 to 0.57 in /fprint-sys

[dependabot-preview]

Updates the requirements on bindgen to permit the latest version.

Changelog

Sourced from bindgen's changelog.

0.57.0

Released 2021/02/01

Added

• Expose module-raw-lines to the CLI (#1936)
• Added an option to fit macro constants to smaller types (#1945)
• Add an option to respect C++ access specifiers on fields (#1968)

Fixed

• Improved C++ auto-detection (#1933)
• Fixed layout of bitfields in some edge cases (#1950)
• Escape the dyn keyword properly (#1951)
• Use absolute paths for unsaved files passed to clang (#1857).

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

---

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).

... (truncated)

Commits

• 5ca2fc7 v0.57.0
• c509ef1 Add failing regression test for #1973.
• e0f06c7 Generate fields as non-pub if they would be access restricted in C++.
• 5177889 Use absolute paths for unsaved files passed to clang and prepend -include dir...
• 9de0d64 Update mdbook
• 922655f ci: update mdbook.
• 8945fa6 book: Touch the book to ensure that GH actions deploy works.
• faf8b3e ci: Move the remaining CI tasks (updating the book) to GitHub actions.
• fde75f6 ci: Switch most CI to GitHub actions.
• afa50fa tests: Remove unnecessary system header include that makes macos unhappy
• Additional commits viewable in compare view

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[dependabot-preview]

Superseded by #8.