HYDRA-142 build pdfjs src on package install

This will run "node make generic" within pdf.js hydra after it is pulled down as a module.

1. This is needed so that the package is usable immediately after install.
2. It allows us to also manually do the pdf.js re-make like this:
   `npm run pdfjs test`  (with the current)
   `npm run pdfjs install` (if we change it from "test" to "install" like below)

@jonmccracken-wf 
@ryanjackson-wf 
@bovardtiberi-wf