6s~10s increase in compile time

[davatron5000]

After installing jekyll-babel, I noticed a 6s~10s jump in compile time. I was able to isolate the performance regression to jekyll-babel by creating a new project and creating a single JS file, then copying it over and over.

---
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let foo = "bar";

Even with this simple file, there was a +500ms increase in compile time per JS file (4 files == 2s increase).

Thoughts? Any way to make this faster? Thanks.