Update Decimal dependency to 3.x

[ccarvalho-eng]

Pins Decimal to 3.1.0.

This keeps the package on a patched Decimal release and avoids the 3.0.0 regression noted in ericmj/decimal#228.

Verification:

• mix test

[GRoguelon]

I would recommend to install >= 3.0.1, there is a bug in 3.0.0 which causes an infinity loop when passing Decimal.new("0.0") to Number.

Source:

• Fix infinite loop in to_integer/1 for zero coefficient ericmj/decimal#229
• Infinite loop in strip_trailing_zeros_one/2 when coefficient is 0 ericmj/decimal#228

[ccarvalho-eng]

Thanks for pointing that out. I updated the PR to pin Decimal to 3.1.0, so it avoids the 3.0.0 issue entirely. I reran mix test successfully after the change.