Add Vim filetype to direnv's .envrc files.

.config/git/skel/.envrc

 # shellcheck shell=bash disable=SC1091
+# vim: ft=sh
 source_up
 [ ! -f .envrc.private ] || . .envrc.private

Repositories/SchooLinks/.envrc

 # shellcheck shell=bash disable=SC1091
+# vim: ft=sh
 source_up
 export GIT_AUTHOR_EMAIL='nimrod@schoolinks.com'
 export GIT_AUTHOR_NAME='Nimrod Adar'