Always determine `tern-project-dir' just-in-time
Always determine `tern-project-dir' just-in-time

Fixes https://github.com/ternjs/tern/issues/756

ternjs/tern,ternjs/tern,othree/tern,MarcelGerber/tern,ternjs/tern,othree/tern,fileability/tern,neoclide/tern,neoclide/tern,fileability/tern,marijnh/tern,neoclide/tern,othree/tern,emacsmirror/tern,MarcelGerber/tern,fileability/tern,marijnh/tern,MarcelGerber/tern,emacsmirror/tern,marijnh/tern,emacsmirror/tern