Update linked-hash-map to avoid UB

[expenses]

I've been running into contain-rs/linked-hash-map#106 while trying to get https://github.com/wahn/rs_pbrt. This PR updates linked-hash-map and fixes that issue.

thread 'main' panicked at 'attempted to leave type `linked_hash_map::Node<std::string::String, ply_rs::ply::ElementDef>` uninitialized, which is invalid', /rustc/2fd73fabe469357a12c2c974c140f67e7cdd76d0/library/core/src/mem/mod.rs:671:9
stack backtrace:
   0: rust_begin_unwind
             at /rustc/2fd73fabe469357a12c2c974c140f67e7cdd76d0/library/std/src/panicking.rs:493:5
   1: core::panicking::panic_fmt
             at /rustc/2fd73fabe469357a12c2c974c140f67e7cdd76d0/library/core/src/panicking.rs:92:14
   2: core::panicking::panic
             at /rustc/2fd73fabe469357a12c2c974c140f67e7cdd76d0/library/core/src/panicking.rs:50:5
   3: <linked_hash_map::LinkedHashMap<alloc::string::String,V> as ply_rs::ply::key_map::Addable<V>>::add
   4: rs_pbrt::shapes::plymesh::create_ply_mesh
   5: rs_pbrt::core::api::get_shapes_and_materials
   6: rs_pbrt::core::api::pbrt_shape
   7: rs_pbrt::parse_line
   8: rs_pbrt::parse_file
   9: rs_pbrt::main