Dependency 'github.com/cznic/mathutil' is outdated.

[chaicho]

Is your enhancement proposal related to a problem? Please describe.

Currently gleam relys on github.com/cznic/mathutil. But its outdated and was moved to moved to modernc.org/mathutil (vcs) as can be seen from https://github.com/cznic/mathutil.

Describe the solution you'd like

Replace cznic/mathutil with modernc.org/mathutil.

[chrislusf]

Thanks! Do you plan to send a PR?