Make term-test dependency optional

checkPhase still requires term-test

Closes #1

default.nix

@@ -1,4 +1,9 @@
-{ stdenv, direnv, term-test }:
+{ stdenv
+, direnv
+, term-test ? null
+, doCheck ? true
+}:
+assert doCheck -> term-test != null;
 
 stdenv.mkDerivation {
   name = "direnv-cache";
@@ -8,6 +13,6 @@ stdenv.mkDerivation {
     make install PREFIX=$out
   '';
   checkInputs = [ term-test ];
-  doCheck = true;
+  inherit doCheck;
   passthru = { direnvrc = ./direnvrc; };
 }