Don't blow up dotenv for users who don't have nix

.envrc

@@ -3,7 +3,7 @@
 
 if type -P lorri &>/dev/null; then
   eval "$(lorri direnv)"
-else
+elif type -P nix-shell &>/dev/null; then
   echo 'while direnv evaluated .envrc, could not find the command "lorri" [https://github.com/nix-community/lorri]'
   use nix
 fi