clerk helper: Use new API

While testing for #160 I did the following patch to `clerk_helper.clj` to use clerk's new API: https://github.com/scicloj/wolframite/commit/34269ee55c403e8cd16ceec440c417a18156a81c#diff-946fa43fc736954a9adbcfc6e71c895afb8465243217b84db1052d3bcf4e5c12 Would you be open for a PR for this or just apply this yourselves?