Merge pull request ethereum#6690 from zjiekai/patch-4

fix frontier-thawing blog post links

src/content/history/index.md

@@ -394,8 +394,8 @@ The Homestead fork that looked to the future. It included several protocol chang
 
 The frontier thawing fork lifted the 5,000 [gas](/glossary/#gas) limit per [block](/glossary/#block) and set the default gas price to 51 [gwei](/glossary/#gwei). This allowed for transactions – transactions require 21,000 gas. The [difficulty bomb](/glossary/#difficulty-bomb) was introduced to ensure a future hard-fork to [proof-of-stake](/glossary/#pos).
 
-[Read the Ethereum Foundation announcement](https://blog.ethereum.org/2015/08/04/the-thawing-frontier/)
-[Read the Ethereum Protocol Update 1](https://blog.ethereum.org/2015/08/04/ethereum-protocol-update-1/)
+- [Read the Ethereum Foundation announcement](https://blog.ethereum.org/2015/08/04/the-thawing-frontier/)
+- [Read the Ethereum Protocol Update 1](https://blog.ethereum.org/2015/08/04/ethereum-protocol-update-1/)
 
 ---