Update istanbul.md

Author: davidjsonn

network-upgrades/mainnet-upgrades/istanbul.md

@@ -35,9 +35,9 @@ This meta-EIP specifies the changes included in the Ethereum hardfork named Ista
 
 ## References
 
-1. Included EIPs were finalized in [All Core Devs Call #68](https://github.com/ethereum/pm/blob/master/All%20Core%20Devs%20Meetings/Meeting%2068.md)
+1. Included EIPs were finalized in [All Core Devs Call #68](https://github.com/ethereum/pm/blob/master/AllCoreDevs-EL-Meetings/Meeting%2068.md)
 2. https://medium.com/ethereum-cat-herders/istanbul-testnets-are-coming-53973bcea7df
 
 ## Copyright
 
-Copyright and related rights waived via [CC0](https://creativecommons.org/publicdomain/zero/1.0/).
+Copyright and related rights waived via [CC0](https://creativecommons.org/publicdomain/zero/1.0/).