Gas optimization: Reduce storage write

[code423n4]

Handle

gzeon

Vulnerability details

Proof of Concept

https://github.com/code-423n4/2021-11-yaxis/blob/146febcb61ae7fe20b0920849c4f4bbe111c6ba7/contracts/v3/alchemix/Alchemist.sol#L630
The line can be rewritten as
_remainingAmount = _remainingAmount.add(_borrowFeeAmount);
to reduce a storage write. Alternatively use a memory variable to preserve code readability.