chore: make shellcheck happy

lib-ee/emqx_ee_bridge/i18n/emqx_ee_bridge_cassa.conf

@@ -39,7 +39,7 @@ will be forwarded."""
 
     desc_config {
         desc {
-            en: """Configuration for an Cassandra bridge."""
+            en: """Configuration for a Cassandra bridge."""
             zh: """Cassandra 桥接配置"""
         }
         label: {