Test modulo function behavior, rewrite if necessary

[proan]

The postiveMod() function [https://github.com/grt192/GRT2020Preseason/blob/develop/src/main/java/frc/util/GRTUtil.java#L15] looks like it might have errors.

To check if the behavior is correct, please construct some test cases, where you know the inputs and what the output should be, then try those inputs and see if the outputs match.

If there results do not match, please rewrite the function.