docs: use better translation

lib-ee/emqx_license/i18n/emqx_license_http_api.conf

@@ -13,7 +13,7 @@ emqx_license_http_api {
   desc_license_upload_api {
     desc {
       en: "Upload a license file or key"
-      zh: "上传许可证文件或钥匙"
+      zh: "上传许可证文件或密钥"
     }
     label: {
       en: "Update license"