Merge pull request #2663 from jeannekamikaze/master

Replace 'which'.

Author: carols10cents

src/ch15-04-rc.md

@@ -9,9 +9,9 @@ edges pointing to it.
 
 To enable multiple ownership, Rust has a type called `Rc<T>`, which is an
 abbreviation for *reference counting*. The `Rc<T>` type keeps track of the
-number of references to a value which determines whether or not a value is
-still in use. If there are zero references to a value, the value can be cleaned
-up without any references becoming invalid.
+number of references to a value to determine whether or not the value is still
+in use. If there are zero references to a value, the value can be cleaned up
+without any references becoming invalid.
 
 Imagine `Rc<T>` as a TV in a family room. When one person enters to watch TV,
 they turn it on. Others can come into the room and watch the TV. When the last