rename from _ to -

Author: nikomatsakis

src/SUMMARY.md

@@ -16,19 +16,19 @@
 
 - [Rust 2018](rust-2018/index.md)
   - [Path and module system changes](rust-2018/path-changes.md)
-  - [Anonymous trait function parameters deprecated](rust-2018/trait_fn_parameters.md)
-  - [New keywords](rust-2018/new_keywords.md)
-  - [Method dispatch for raw pointers to inference variables](rust-2018/tyvar_behind_raw_pointer.md)
+  - [Anonymous trait function parameters deprecated](rust-2018/trait-fn-parameters.md)
+  - [New keywords](rust-2018/new-keywords.md)
+  - [Method dispatch for raw pointers to inference variables](rust-2018/tyvar-behind-raw-pointer.md)
   - [Cargo changes](rust-2018/cargo.md)
 
 ## Rust 2021
 
 - [Rust 2021 🚧](rust-2021/index.md)
   - [Additions to the prelude](rust-2021/prelude.md)
-  - [Default Cargo feature resolver](rust-2021/default_cargo_resolver.md)
-  - [IntoIterator for arrays](rust-2021/IntoIterator_for_arrays.md)
-  - [Disjoint capture in closures](rust-2021/disjoint_capture_in_closures.md)
-  - [Panic macro consistency](rust-2021/panic_macro_consistency.md)
-  - [Reserving syntax](rust-2021/reserving_syntax.md)
-  - [Warnings promoted to errors](rust-2021/warnings_promoted_to_error.md)
-  - [Or patterns in macro-rules](rust-2021/or_patterns_macro_rules.md)
+  - [Default Cargo feature resolver](rust-2021/default-cargo-resolver.md)
+  - [IntoIterator for arrays](rust-2021/IntoIterator-for-arrays.md)
+  - [Disjoint capture in closures](rust-2021/disjoint-capture-in-closures.md)
+  - [Panic macro consistency](rust-2021/panic-macro-consistency.md)
+  - [Reserving syntax](rust-2021/reserving-syntax.md)
+  - [Warnings promoted to errors](rust-2021/warnings-promoted-to-error.md)
+  - [Or patterns in macro-rules](rust-2021/or-patterns-macro-rules.md)

src/rust-2018/index.md

@@ -6,4 +6,3 @@
 | Release version | [1.31.0](https://blog.rust-lang.org/2018/12/06/Rust-1.31-and-rust-2018.html) |
 
 The edition system was created for the release of Rust 2018. The release of the Rust 2018 edition coincided with a number of other features all coordinated around the theme of *productivity*. The majority of those features were backwards compatible and are now available on all editions; however, some of those changes required the edition mechanism (most notably the [module system changes](path-changes.md)).
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