book: whitespace

Author: tshepang

src/doc/trpl/documentation.md

@@ -382,7 +382,7 @@ $ rustdoc --test path/to/my/crate/root.rs
 $ cargo test
 ```
 
-That's right, `cargo test` tests embedded documentation too. However, 
+That's right, `cargo test` tests embedded documentation too. However,
 `cargo test` will not test binary crates, only library ones. This is
 due to the way `rustdoc` works: it links against the library to be tested,
 but with a binary, there’s nothing to link to.