Add support for shelf 0.6.0.

lib/src/util/one_off_handler.dart

Index: lib/src/util/one_off_handler.dart
diff --git a/lib/src/util/one_off_handler.dart b/lib/src/util/one_off_handler.dart
index 9994f46ac26cf79246f7025e20333d208d28ad1e..069d6818875d0d4028f022be2d5060cd2537d61a 100644
--- a/lib/src/util/one_off_handler.dart
+++ b/lib/src/util/one_off_handler.dart
@@ -36,8 +36,14 @@ class OneOffHandler {
 
   /// Dispatches [request] to the appropriate handler.
   _onRequest(shelf.Request request) {
-    // Skip the first component because it's always "/".
-    var components = p.url.split(request.url.path).skip(1).toList();
+    var components = p.url.split(request.url.path);
+
+    // For shelf < 0.6.0, the first component of the path is always "/". We can
+    // safely skip it.
+    if (components.isNotEmpty && components.first == "/") {
+      components.removeAt(0);
+    }
+
     if (components.isEmpty) return new shelf.Response.notFound(null);
 
     var handler = _handlers.remove(components.removeAt(0));