pkg/shelf: spelling fixes

lib/src/cascade.dart

Index: lib/src/cascade.dart
diff --git a/lib/src/cascade.dart b/lib/src/cascade.dart
index f4e7cadd57f49de8f191c532bc69ec2b8788ff40..03950899304f392f40d97cb2f6017ae2c3b1084f 100644
--- a/lib/src/cascade.dart
+++ b/lib/src/cascade.dart
@@ -38,7 +38,7 @@ class Cascade {
   ///
   /// If [statusCodes] is passed, responses with those status codes are
   /// considered unacceptable. If [shouldCascade] is passed, responses for which
-  /// it returns `true` are considered unacceptale. [statusCode] and
+  /// it returns `true` are considered unacceptable. [statusCode] and
   /// [shouldCascade] may not both be passed.
   Cascade({Iterable<int> statusCodes, bool shouldCascade(Response response)})
       : _shouldCascade = _computeShouldCascade(statusCodes, shouldCascade),