Fix Decimal can be constructed with a negative atomics

[tien]

No description provided.

[webmaster128]

Nice catch! The atomics string should checked more strictly.

Can you use

    if (!atomics.match(/^[0-9]+$/)) {
      throw new Error("Invalid string format. Only non-negative integers in decimal representation suppored.");
    }

instead?

[tien]

@webmaster128 sure thing, I have updated the PR accordingly.

[webmaster128]

Thank you!

Will merge as part of #1195

[webmaster128]

Shipped as part of CosmJS 0.29.0