Fix some broken links in the book

Author: fhartwig

src/doc/trpl/concurrency.md

@@ -176,8 +176,8 @@ Here's the error:
                   ^~~~~~~~~~~~~
 ```
 
-You see, [`Mutex`](std/sync/struct.Mutex.html) has a
-[`lock`](http://doc.rust-lang.org/nightly/std/sync/struct.Mutex.html#method.lock)
+You see, [`Mutex`](../std/sync/struct.Mutex.html) has a
+[`lock`](../std/sync/struct.Mutex.html#method.lock)
 method which has this signature:
 
 ```ignore

src/doc/trpl/error-handling.md

@@ -297,5 +297,5 @@ It's worth noting that you can only use `try!` from a function that returns a
 `Result`, which means that you cannot use `try!` inside of `main()`, because
 `main()` doesn't return anything.
 
-`try!` makes use of [`From<Error>`](../std/convert/trait.From.hml) to determine
+`try!` makes use of [`From<Error>`](../std/convert/trait.From.html) to determine
 what to return in the error case.

src/doc/trpl/macros.md

@@ -33,7 +33,7 @@ mind.
 You may have seen the `vec!` macro, used to initialize a [vector][] with any
 number of elements.
 
-[vector]: arrays-vectors-and-slices.html
+[vector]: vectors.html
 
 ```rust
 let x: Vec<u32> = vec![1, 2, 3];