pkg/shelf: add travis and code coverage settings

test/test_all.dart

+import 'package:unittest/unittest.dart';
+
+import 'cascade_test.dart' as cascade;
+import 'create_middleware_test.dart' as create_middleware;
+import 'hijack_test.dart' as hijack;
+import 'log_middleware_test.dart' as log_middleware;
+import 'message_change_test.dart' as message_change;
+import 'message_test.dart' as message;
+import 'pipeline_test.dart' as pipeline;
+import 'request_test.dart' as request;
+import 'response_test.dart' as response;
+import 'shelf_io_test.dart' as shelf_io;
+
+void main() {
+  group('cascade', cascade.main);
+  group('create_middleware', create_middleware.main);
+  group('hijack', hijack.main);
+  group('log_middleware', log_middleware.main);
+  group('message_change', message_change.main);
+  group('message', message.main);
+  group('pipeline', pipeline.main);
+  group('request', request.main);
+  group('response', response.main);
+  group('shelf_io', shelf_io.main);
+}