Fix table for withdrawal credentials prefixes

Minor cosmetic fixes (misformated table, section title).

specs/phase0/beacon-chain.md

@@ -14,7 +14,7 @@
   - [Misc](#misc)
   - [Gwei values](#gwei-values)
   - [Initial values](#initial-values)
-  - [Validator withdrawal credential versions](#validator-withdrawal-credential-versions)
+  - [Withdrawal credentials prefixes](#withdrawal-credentials-prefixes)
   - [Time parameters](#time-parameters)
   - [State list lengths](#state-list-lengths)
   - [Rewards and penalties](#rewards-and-penalties)
@@ -212,8 +212,10 @@ The following values are (non-configurable) constants used throughout the specif
 | - | - |
 | `GENESIS_FORK_VERSION` | `Version('0x00000000')` |
 
-### Validator withdrawal credential versions
+### Withdrawal credentials prefixes
 
+| Name | Value |
+| - | - |
 | `BLS_WITHDRAWAL_PREFIX` | `Bytes1('0x00')` |
 | `ETH1_ADDRESS_WITHDRAWAL_PREFIX` | `Bytes1('0x01')` |