Fix all strong mode warnings.

lib/src/version.dart

 // Copyright (c) 2014, 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.
 
 import 'dart:math' as math;
 
-import 'package:collection/equality.dart';
+import 'package:collection/collection.dart';
 
 import 'patterns.dart';
 import 'version_constraint.dart';
 import 'version_range.dart';
 
 /// The equality operator to use for comparing version components.
 final _equality = const IterableEquality();
 
 /// A parsed semantic version number.
 class Version implements Comparable<Version>, VersionConstraint, VersionRange {
@@ skipping 300 matching lines @@
           // Compare two strings.
           return aPart.compareTo(bPart);
         }
       }
     }
 
     // The lists are entirely equal.
     return 0;
   }
 }