add "pragma solidity ^0.4.0;" to code examples

docs/common-patterns.rst

@@ -28,6 +28,8 @@ become the new richest.
 
 ::
 
+    pragma solidity ^0.4.0;
+
     contract WithdrawalContract {
         address public richest;
         uint public mostSent;
@@ -68,6 +70,8 @@ This is as opposed to the more intuitive sending pattern.
 
 ::
 
+    pragma solidity ^0.4.0;
+
     contract SendContract {
         address public richest;
         uint public mostSent;
@@ -131,6 +135,8 @@ restrictions highly readable.
 
 ::
 
+    pragma solidity ^0.4.0;
+
     contract AccessRestriction {
         // These will be assigned at the construction
         // phase, where `msg.sender` is the account
@@ -270,6 +276,8 @@ function finishes.
 
 ::
 
+    pragma solidity ^0.4.0;
+
     contract StateMachine {
         enum Stages {
             AcceptingBlindedBids,