Update exception-safety.md

Author: DaseinPhaos

src/exception-safety.md

@@ -137,7 +137,7 @@ If Rust had `try` and `finally` like in Java, we could do the following:
 bubble_up(heap, index):
     let elem = heap[index]
     try:
-        while index != 0 && element < heap[parent(index)]:
+        while index != 0 && elem < heap[parent(index)]:
             heap[index] = heap[parent(index)]
             index = parent(index)
     finally: