Updated the config docs

Author: botahamec

book/src/lint_configuration.md

@@ -130,6 +130,7 @@ Suppress lints whenever the suggested change would cause breakage for other crat
 * [option_option](https://rust-lang.github.io/rust-clippy/master/index.html#option_option)
 * [linkedlist](https://rust-lang.github.io/rust-clippy/master/index.html#linkedlist)
 * [rc_mutex](https://rust-lang.github.io/rust-clippy/master/index.html#rc_mutex)
+* [unnecessary_box_returns](https://rust-lang.github.io/rust-clippy/master/index.html#unnecessary_box_returns)
 
 
 ### msrv

clippy_lints/src/utils/conf.rs

@@ -249,7 +249,7 @@ define_Conf! {
     /// arithmetic-side-effects-allowed-unary = ["SomeType", "AnotherType"]
     /// ```
     (arithmetic_side_effects_allowed_unary: rustc_data_structures::fx::FxHashSet<String> = <_>::default()),
-    /// Lint: ENUM_VARIANT_NAMES, LARGE_TYPES_PASSED_BY_VALUE, TRIVIALLY_COPY_PASS_BY_REF, UNNECESSARY_WRAPS, UNUSED_SELF, UPPER_CASE_ACRONYMS, WRONG_SELF_CONVENTION, BOX_COLLECTION, REDUNDANT_ALLOCATION, RC_BUFFER, VEC_BOX, OPTION_OPTION, LINKEDLIST, RC_MUTEX.
+    /// Lint: ENUM_VARIANT_NAMES, LARGE_TYPES_PASSED_BY_VALUE, TRIVIALLY_COPY_PASS_BY_REF, UNNECESSARY_WRAPS, UNUSED_SELF, UPPER_CASE_ACRONYMS, WRONG_SELF_CONVENTION, BOX_COLLECTION, REDUNDANT_ALLOCATION, RC_BUFFER, VEC_BOX, OPTION_OPTION, LINKEDLIST, RC_MUTEX, UNNECESSARY_BOX_RETURNS.
     ///
     /// Suppress lints whenever the suggested change would cause breakage for other crates.
     (avoid_breaking_exported_api: bool = true),