fix shelf_static by pinning to v0.2.1

DEPS

 # Copyright (c) 2012, 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.
 
 vars = {
   # The dart_root is the root of our sdk checkout. This is normally
   # simply sdk, but if using special gclient specs it can be different.
   "dart_root": "sdk",
 
   # The svn location to pull out dependencies from
@@ skipping 74 matching lines @@
   "pool_rev": "@22e12aeb16ad0b626900dbe79e4a25391ddfb28c",
   "pub_rev": "@9d707158fedc86fc2b02f62cdfe804902b098d9d",
   "pub_cache_tag": "@v0.0.1+2",
   "pub_semver_tag": "@1.2.1",
   "quiver_tag": "@0.21.4",
   "scheduled_test_tag": "@0.11.8+1",
   "shelf_rev": "@1e87b79b21ac5e6fa2f93576d6c06eaa65285ef4",
   "smoke_rev" : "@f3361191cc2a85ebc1e4d4c33aec672d7915aba9",
   "source_maps_rev": "@379b4f31c4e2987eb15934d1ad8b419c6cc897b3",
   "sqlite_rev": "@38811b79f42801662adc0458a25270ab690a6b81",
-  "shelf_static_rev": "@0.2.2",
+  "shelf_static_rev": "@v0.2.1",
   "shelf_web_socket_rev": "@ff170cec2c0e4e5722cdf47c557be63b5035a602",
   "source_span_rev": "@42501132e43599a151ba6727d340e44442f86c05",
   "stack_trace_tag": "@1.2.1",
   "string_scanner_rev": "@3e7617d6f74ba382e9b6130b1cc12091d89a9bc5",
   "sunflower_rev": "@879b704933413414679396b129f5dfa96f7a0b1e",
   "test_tag": "@0.12.1",
   "test_reflective_loader_tag": "@0.0.3",
   "utf_rev": "@1f55027068759e2d52f2c12de6a57cce5f3c5ee6",
   "unittest_tag": "@0.11.6",
   "usage_rev": "@b5080dac0d26a5609b266f8fdb0d053bc4c1c638",
@@ skipping 261 matching lines @@
       '--no_resume',
       '--bucket',
       'dart-dependencies',
       '-d',
       '-r',
       Var('dart_root') + '/third_party/d8',
     ],
   },
 
 ]