auto merge of #14357 : huonw/rust/spelling, r=pnkfelix

The span on a inner doc-comment would point to the next token, e.g. the span for the `a` line points to the `b` line, and the span of `b` points to the `fn`.

```rust
//! a
//! b

fn bar() {}
```

src/libstd/io/stdio.rs

@@ -92,7 +92,7 @@ fn src<T>(fd: libc::c_int, readable: bool, f: |StdSource| -> T) -> T {
 /// provided unbuffered access to stdin.
 ///
 /// Care should be taken when creating multiple handles to the stdin of a
-/// process. Beause this is a buffered reader by default, it's possible for
+/// process. Because this is a buffered reader by default, it's possible for
 /// pending input to be unconsumed in one reader and unavailable to other
 /// readers. It is recommended that only one handle at a time is created for the
 /// stdin of a process.