Merge branch 'release-v2.0.0' of github.com:OpenZeppelin/openzeppelin-solidity into release-v2.0.0

contracts/payment/Escrow.sol

@@ -45,7 +45,6 @@ contract Escrow is Initializable, Secondary {
   */
   function withdraw(address payee) public onlyPrimary {
     uint256 payment = _deposits[payee];
-    assert(address(this).balance >= payment);
 
     _deposits[payee] = 0;
 

contracts/payment/SplitPayment.sol

@@ -86,7 +86,6 @@ contract SplitPayment is Initializable {
     );
 
     require(payment != 0);
-    assert(address(this).balance >= payment);
 
     _released[account] = _released[account].add(payment);
     _totalReleased = _totalReleased.add(payment);