FastLinearAlgebra: fixed issue for characteristic 2 FFPACK field

Hello Mike,

i fixed the fixed issue for the characteristic 2 FFPACK field by using Modular
instead of ModularBalanced .
On my machine I also observe some failing unit tests
(
cd Macaulay2/e/unit_test
make failing # ARingRRR.multDivide fails
)

Best,

Jakob