Merge pull request #1449 from devoncarew/trace_command

update description text for the trace command

packages/flutter_tools/lib/src/commands/trace.dart

@@ -11,9 +11,9 @@ import '../runner/flutter_command.dart';
 
 class TraceCommand extends FlutterCommand {
   final String name = 'trace';
-  final String description = 'Start and stop tracing a running Flutter app '
-      '(Android only, requires root).\n'
-      'To start a trace, wait, and then stop the trace, don\'t set any flags '
+  final String description = 'Start and stop tracing for a running Flutter app '
+      '(Android only).\n'
+      'To start a trace, wait, then stop the trace, don\'t set any flags '
       'except (optionally) duration.\n'
       'Otherwise, specify either start or stop to manually control the trace.';