update required geth version

Author: iurimatias

README.md

@@ -38,7 +38,7 @@ Table of Contents
 
 Installation
 ======
-Requirements: geth (1.4.4 or higher), node (5.0.0) and npm
+Requirements: geth (1.5.5 or higher), node (5.0.0) and npm
 Optional: serpent (develop) if using contracts with Serpent, testrpc or ethersim if using the simulator or the test functionality.
 Further: depending on the dapp stack you choose: [IPFS](https://ipfs.io/)