vm: use truncated division in MOD

[fyrchik]

Mimic C#'s % behavior. https://dotnetfiddle.net/BaVazY
Related 4b44190 (#773).

[codecov]

Codecov Report

Merging #826 into master will not change coverage by %.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #826   +/-   ##
=======================================
  Coverage   67.65%   67.65%           
=======================================
  Files         141      141           
  Lines       13163    13163           
=======================================
  Hits         8906     8906           
  Misses       3849     3849           
  Partials      408      408           

Impacted Files	Coverage Δ
pkg/vm/vm.go	77.99% <100.00%> (ø)

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