TRPL: Fix two typos

src/doc/trpl/error-handling.md

@@ -154,7 +154,7 @@ fn find(haystack: &str, needle: char) -> Option<usize> {
 }
 ```
 
-Notice that when this function finds a matching character, it doen't just
+Notice that when this function finds a matching character, it doesn't just
 return the `offset`. Instead, it returns `Some(offset)`. `Some` is a variant or
 a *value constructor* for the `Option` type. You can think of it as a function
 with the type `fn<T>(value: T) -> Option<T>`. Correspondingly, `None` is also a
@@ -840,7 +840,7 @@ example, the very last call to `map` multiplies the `Ok(...)` value (which is
 an `i32`) by `2`. If an error had occurred before that point, this operation
 would have been skipped because of how `map` is defined.
 
-`map_err` is the trick the makes all of this work. `map_err` is just like
+`map_err` is the trick that makes all of this work. `map_err` is just like
 `map`, except it applies a function to the `Err(...)` value of a `Result`. In
 this case, we want to convert all of our errors to one type: `String`. Since
 both `io::Error` and `num::ParseIntError` implement `ToString`, we can call the