Update EIP-663: Fix markdown rendering 2

Merged by EIP-Bot.

EIPS/eip-663.md

@@ -50,7 +50,7 @@ If the code is valid EOF1, the following rules apply:
 4. Execution rules:
    1. `DUPN`: the `n`'th stack item is duplicated at the top of the stack. (*Note: We use 1-based indexing here.*)
    2. `SWAPN`: the `n + 1`'th stack item is swapped with the top of the stack.
-   3  `EXCHANGE`: the `n + 1`'th stack item is swapped with the `n + m + 1`'th stack item.
+   3. `EXCHANGE`: the `n + 1`'th stack item is swapped with the `n + m + 1`'th stack item.
 
 The gas cost for all three instructions is set at 3.