fix typos (#390)

src/idioms/deref.md

@@ -27,7 +27,7 @@ impl<T> Deref for Vec<T> {
 
 A `Vec<T>` is an owning collection of `T`s, while a slice (`&[T]`) is a borrowed
 collection of `T`s. Implementing `Deref` for `Vec` allows implicit dereferencing
-from `&Vec<T>` to `&[T]` and includes the relationship in auto-derefencing
+from `&Vec<T>` to `&[T]` and includes the relationship in auto-dereferencing
 searches. Most methods you might expect to be implemented for `Vec`s are instead
 implemented for slices.
 

src/idioms/ffi/errors.md

@@ -4,7 +4,7 @@
 
 In foreign languages like C, errors are represented by return codes. However,
 Rust's type system allows much more rich error information to be captured and
-propogated through a full type.
+propagated through a full type.
 
 This best practice shows different kinds of error codes, and how to expose them
 in a usable way:

src/patterns/behavioural/command.md

@@ -205,7 +205,7 @@ fn main() {
 If our commands are small and may be defined as functions or passed as a closure
 then using function pointers might be preferable since it does not exploit
 dynamic dispatch. But if our command is a whole struct with a bunch of functions
-and variables defined as seperated module then using trait objects would be more
+and variables defined as separated module then using trait objects would be more
 suitable. A case of application can be found in [`actix`](https://actix.rs/),
 which uses trait objects when it registers a handler function for routes. In
 case of using `Fn` trait objects we can create and use commands in the same way