fix test suit

test/fast/Unit tests/nvm_ls_current

@@ -12,8 +12,8 @@ TEST_PWD=$(pwd)
 TEST_DIR="$TEST_PWD/nvm_ls_current_tmp"
 rm -rf "$TEST_DIR"
 mkdir "$TEST_DIR"
-ln -s "$(which which)" "$TEST_DIR/which"
-ln -s "$(which dirname)" "$TEST_DIR/dirname"
+ln -s "$(command which which)" "$TEST_DIR/which"
+ln -s "$(command which dirname)" "$TEST_DIR/dirname"
 
 [ "$(PATH="$TEST_DIR" nvm_ls_current)" = "none" ] || die 'when node not installed, nvm_ls_current did not return "none"'
 [ "@$(PATH="$TEST_DIR" nvm_ls_current 2> /dev/stdout 1> /dev/null)@" = "@@" ] || die 'when node not installed, nvm_ls_current returned error output'