Update EIP to refer to Ethereum Mainnet, wording as per EIP-2228 (#4538)

Author: fulldecent

EIPS/eip-1679.md

@@ -18,7 +18,7 @@ This meta-EIP specifies the changes included in the Ethereum hardfork named Ista
 - Codename: Istanbul
 
 ### Activation
-  - `Block >= 9,069,000` on the Ethereum mainnet
+  - `Block >= 9,069,000` on the Ethereum Mainnet
   - `Block >= 6,485,846` on the Ropsten testnet
   - `Block >= 14,111,141` on the Kovan testnet
   - `Block >= 5,435,345` on the Rinkeby testnet