docs: improve language in methods-and-traits section (#2881)

I asked Gemini to review the English for inconsistencies and grammar
mistakes. This is the result and I hope it's useful!

As a non-native speaker, it is hard for me to evaluate the finer
details, so let me know if you would like to see changes (or even
better: make them directly in the PR with the suggestion function).

---------

Co-authored-by: Dmitri Gribenko <gribozavr@gmail.com>

src/methods-and-traits/deriving.md

@@ -30,7 +30,7 @@ fn main() {
   macros to add useful functionality. For example, `serde` can derive
   serialization support for a struct using `#[derive(Serialize)]`.
 
-- Derivation is usually provided for traits that have a common boilerplate-y
+- Derivation is usually provided for traits that have a common boilerplate
   implementation that is correct for most cases. For example, demonstrate how a
   manual `Clone` impl can be repetitive compared to deriving the trait:
 

src/methods-and-traits/exercise.md

@@ -5,7 +5,7 @@ minutes: 15
 # Exercise: Logger Trait
 
 Let's design a simple logging utility, using a trait `Logger` with a `log`
-method. Code which might log its progress can then take an `&impl Logger`. In
+method. Code that might log its progress can then take an `&impl Logger`. In
 testing, this might put messages in the test logfile, while in a production
 build it would send messages to a log server.
 

src/methods-and-traits/methods.md

@@ -65,7 +65,7 @@ There are several common receivers for a method:
   transmitted. Complete ownership does not automatically mean mutability.
 - `mut self`: same as above, but the method can mutate the object.
 - No receiver: this becomes a static method on the struct. Typically used to
-  create constructors which are called `new` by convention.
+  create constructors that are called `new` by convention.
 
 <details>
 

src/methods-and-traits/traits/associated-types.md

@@ -1,6 +1,6 @@
 # Associated Types
 
-Associated types are placeholder types which are supplied by the trait
+Associated types are placeholder types that are supplied by the trait
 implementation.
 
 ```rust,editable