Fix "illegal cpu instruction" in vec-alloc.md

As per #132

src/vec-alloc.md

@@ -37,8 +37,8 @@ that, we'll need to use the rest of the heap APIs. These basically allow us to
 talk directly to Rust's allocator (jemalloc by default).
 
 We'll also need a way to handle out-of-memory (OOM) conditions. The standard
-library calls `std::alloc::oom()`, which in turn calls the the `oom` langitem.
-By default this just aborts the program by executing an illegal cpu instruction.
+library calls `std::alloc::oom()`, which in turn calls the the `oom` langitem,
+which aborts the program in a platform-specific manner.
 The reason we abort and don't panic is because unwinding can cause allocations
 to happen, and that seems like a bad thing to do when your allocator just came
 back with "hey I don't have any more memory".