[analysis_server] Remove added space.

Change-Id: I7a5c8fdfc318359904b9c4befe07ff0be186b446
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/154125
Auto-Submit: Mike Fairhurst <[email protected]>
Commit-Queue: Brian Wilkerson <[email protected]>
Reviewed-by: Brian Wilkerson <[email protected]>

Author: MichaelRFairhurst

pkg/analysis_server/lib/src/plugin/plugin_manager.dart

@@ -221,7 +221,7 @@ abstract class PluginInfo {
         // Plugin crashed, nothing to do.
         return Future<void>.value(null);
       }
-      throw StateError('Cannot stop a plugin that is not running. ');
+      throw StateError('Cannot stop a plugin that is not running.');
     }
     var doneFuture = currentSession.stop();
     currentSession = null;