add solidity pragma to demo and test contracts

demo/app/contracts/simple_storage.sol

@@ -1,3 +1,4 @@
+pragma solidity ^0.4.2;
 contract SimpleStorage {
   uint public storedData;
 

test/contracts/simple_storage.sol

@@ -1,3 +1,4 @@
+pragma solidity ^0.4.2;
 contract SimpleStorage {
   uint public storedData;
 

test/contracts/token.sol

@@ -1,5 +1,6 @@
 // https://github.com/nexusdev/erc20/blob/master/contracts/base.sol
 
+pragma solidity ^0.4.2;
 contract Token {
 
   event Transfer(address indexed from, address indexed to, uint value);