Use correct expansions in install

Author: gagik

.evergreen/evergreen.yml.in

@@ -1138,7 +1138,7 @@ tasks:
       - func: checkout
       - func: install
         vars:
-          node_js_version: ${nVersion}
+          node_js_version: ${node_js_version}
       - func: test
         vars:
           mongosh_server_test_version: ${mongosh_server_test_version}