make constructors internal of abstract contracts

contracts/common/Controlled.sol

@@ -10,7 +10,7 @@ contract Controlled {
 
     address public controller;
 
-    constructor() public { 
+    constructor() internal { 
         controller = msg.sender; 
     }
 

contracts/common/Owned.sol

@@ -14,7 +14,7 @@ contract Owned {
     address public owner;
 
     /// @notice The Constructor assigns the message sender to be `owner`
-    constructor() public {
+    constructor() internal {
         owner = msg.sender;
     }