Improve string resource

Author: Jack251970

Plugins/Flow.Launcher.Plugin.PluginsManager/Languages/en.xaml

@@ -47,7 +47,7 @@
     <system:String x:Key="plugin_pluginsmanager_plugin_modified_error">Plugin {0} has already been modified. Please restart Flow before making any further changes.</system:String>
 
     <system:String x:Key="plugin_pluginsmanager_invalid_zip_title">Invalid zip installer file</system:String>
-    <system:String x:Key="plugin_pluginsmanager_invalid_zip_subtitle">Please check if there is plugin.json in {0}</system:String>
+    <system:String x:Key="plugin_pluginsmanager_invalid_zip_subtitle">Please check if there is a plugin.json in {0}</system:String>
 
     <!--  Plugin Infos  -->
     <system:String x:Key="plugin_pluginsmanager_plugin_name">Plugins Manager</system:String>