update conditionals so that web usages dont accidentally use the node package

pkgs/glob/lib/src/io.dart

diff --git a/pkgs/glob/lib/src/io.dart b/pkgs/glob/lib/src/io.dart
index 32a30d3..20e532b 100644
--- a/pkgs/glob/lib/src/io.dart
+++ b/pkgs/glob/lib/src/io.dart
@@ -4,4 +4,8 @@
 
 // These libraries don't expose *exactly* the same API, but they overlap in all
 // the cases we care about.
-export 'dart:io' if (dart.library.js) 'package:node_io/node_io.dart';
+export 'io_export.dart'
+    // We don't actually support the web - exporting dart:io gives a reasonably
+    // clear signal to users about that since it doesn't exist.
+    if (dart.library.html) 'io_export.dart'
+    if (dart.library.js) 'package:node_io/node_io.dart';

pkgs/glob/lib/src/io_export.dart

diff --git a/pkgs/glob/lib/src/io_export.dart b/pkgs/glob/lib/src/io_export.dart
new file mode 100644
index 0000000..7f339cf
--- /dev/null
+++ b/pkgs/glob/lib/src/io_export.dart
@@ -0,0 +1,9 @@
+// Copyright (c) 2019, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+/// This library exists only to satisfy build_runner, which doesn't allow
+/// sdk libraries to be conditional imported or exported directly.
+library glob.src.io_export;
+
+export 'dart:io';