[shellcheck] disable "Check exit code directly" warning on line 273, 666

We need to use both the exit state and result form the previous commit,
so SC2181 should be disabled here.

nvm.sh

@@ -269,6 +269,7 @@ nvm_ensure_version_installed() {
   local NVM_VERSION_DIR
   if [ "${EXIT_CODE}" != "0" ] || ! nvm_is_version_installed "${LOCAL_VERSION}"; then
     VERSION="$(nvm_resolve_alias "${PROVIDED_VERSION}")"
+    # shellcheck disable=SC2181
     if [ $? -eq 0 ]; then
       nvm_err "N/A: version \"${PROVIDED_VERSION} -> ${VERSION}\" is not yet installed."
       nvm_err ""
@@ -663,6 +664,7 @@ nvm_alias() {
 nvm_ls_current() {
   local NVM_LS_CURRENT_NODE_PATH
   NVM_LS_CURRENT_NODE_PATH="$(command which node 2> /dev/null)"
+  # shellcheck disable=SC2181
   if [ $? -ne 0 ]; then
     nvm_echo 'none'
   elif nvm_tree_contains_path "$(nvm_version_dir iojs)" "${NVM_LS_CURRENT_NODE_PATH}"; then