Add directory check

Author: sfc-gh-astachowski

lib/authentication/secure_storage/json_credential_manager.js

@@ -71,6 +71,9 @@ function JsonCredentialManager(credentialCacheDir, timeoutMs = 60000) {
         await fs.mkdir(cacheDir, options);
         return true;
       } else {
+        if (!stat.isDirectory()) {
+          return false;
+        }
         if (process.platform === 'win32') {
           return true;
         }