[readme] Avoid infinite loop in cdnvm()

Author: tim-connolly

README.md

@@ -524,7 +524,7 @@ Put the following at the end of your `$HOME/.bashrc`:
 
 ```bash
 cdnvm() {
-    cd "$@";
+    command cd "$@";
     nvm_path=$(nvm_find_up .nvmrc | tr -d '\n')
 
     # If there are no .nvmrc file, use the default nvm version