Fix bug and remove duplicate Safe math

EIP20Interface.sol

@@ -2,25 +2,6 @@
 // https://github.com/ethereum/EIPs/blob/master/EIPS/eip-20.md
 pragma solidity ^0.4.19;
 
-library SafeMath {
-    function add(uint a, uint b) internal pure returns (uint c) {
-        c = a + b;
-        require(c >= a);
-    }
-    function sub(uint a, uint b) internal pure returns (uint c) {
-        require(b <= a);
-        c = a - b;
-    }
-    function mul(uint a, uint b) internal pure returns (uint c) {
-        c = a * b;
-        require(a == 0 || c / a == b);
-    }
-    function div(uint a, uint b) internal pure returns (uint c) {
-        require(b > 0);
-        c = a / b;
-    }
-}
-
 contract EIP20Interface {
     uint256 public totalSupply;
     function balanceOf(address _owner) public view returns (uint256 balance);

Svandis.sol

@@ -49,7 +49,7 @@ contract Svandis is EIP20Interface {
         balances[_to] = balances[_to].add(_value);
         balances[_from] = balances[_from].sub(_value);
         if (allowance < MAX_UINT256) {
-            allowed[_from][msg.sender].sub(_value);
+            allowed[_from][msg.sender] = allowed[_from][msg.sender].sub(_value);
         }
         emit Transfer(_from, _to, _value);
         return true;