Merge pull request #64 from kimond/patch-1

Fix typo in object-orientation.md

src/object-orientation.md

@@ -179,7 +179,7 @@ What can I say? It quacks, it must be a duck. What's interesting is that you can
 to any Rust value, not just 'objects'. (Since `quack` is passed a reference, there's an explicit
 dereference `*` to get the integer.)
 
-However, you can't do this with a trait and a type from the same crate, so the standard library
+However, you can only do this with a trait and a type from the same crate, so the standard library
 cannot be 'monkey patched', which is another piece of Ruby folk practice (and not the most wildly
 admired either.)