Replace `$` functor with new syntax `autoinc()`. (#244)
Replace `$` functor with new syntax `autoinc()`. (#244)

Between our previous and current version of Souffle, Souffle renamed the
`$` functor to `autoinc()`. While the `$` synatx still works, it
generates annoying warnings. This commit replaces the one usage of `$`
with `autoinc()`, thus getting rid of those warnings. This fixes #237.
google-research/raksha,google-research/raksha,google-research/raksha,google-research/raksha