contracts mocks: replace deprecated constant with view (#931)

.soliumrc.json

@@ -6,6 +6,7 @@
     "no-empty-blocks": "off",
     "indentation": ["error", 2],
     "arg-overflow": ["warning", 3],
+    "no-constant": ["error"],
     "security/enforce-explicit-visibility": ["error"],
     "security/no-block-members": ["warning"],
     "security/no-inline-assembly": ["warning"]

contracts/mocks/SafeERC20Helper.sol

@@ -21,11 +21,11 @@ contract ERC20FailingMock is ERC20 {
     return false;
   }
 
-  function balanceOf(address) public constant returns (uint256) {
+  function balanceOf(address) public view returns (uint256) {
     return 0;
   }
 
-  function allowance(address, address) public constant returns (uint256) {
+  function allowance(address, address) public view returns (uint256) {
     return 0;
   }
 }
@@ -48,11 +48,11 @@ contract ERC20SucceedingMock is ERC20 {
     return true;
   }
 
-  function balanceOf(address) public constant returns (uint256) {
+  function balanceOf(address) public view returns (uint256) {
     return 0;
   }
 
-  function allowance(address, address) public constant returns (uint256) {
+  function allowance(address, address) public view returns (uint256) {
     return 0;
   }
 }