Update EIP-8141: fix typos

Merged by EIP-Bot.

Author: fjl

EIPS/eip-8141.md

@@ -65,7 +65,7 @@ There are three modes:
 |    1 | `VERIFY`       | Frame identifies as transaction validation                |
 |    2 | `SENDER`       | Execute frame as `sender`                                 |
 
-#### `DEFAULT` Mode
+##### `DEFAULT` Mode
 
 Frame executes as regular call where the caller address is `ENTRY_POINT`.
 
@@ -112,7 +112,8 @@ With the frame transaction, the signature may be at an arbitrary location in the
 ```python
 def compute_sig_hash(tx: FrameTx) -> Hash:
     for i, frame in enumerate(tx.frames):
-        tx.frames[i].data = Bytes()
+        if frame.mode == VERIFY:
+            tx.frames[i].data = Bytes()
     return keccak(rlp(tx))
 ```