Fix --offline with prerelease versions.

lib/src/source/hosted.dart

Index: lib/src/source/hosted.dart
diff --git a/lib/src/source/hosted.dart b/lib/src/source/hosted.dart
index e1cde6365633076f18ec3277d567c04fbb41c14c..6971e54a8310727efb5a503f81d8ce07b4154b2c 100644
--- a/lib/src/source/hosted.dart
+++ b/lib/src/source/hosted.dart
@@ -271,7 +271,7 @@ class OfflineHostedSource extends HostedSource {
         var components = path.basename(entry).split("-");
         if (components.first != ref.name) return null;
         return HostedSource.idFor(
-            ref.name, new Version.parse(components.last),
+            ref.name, new Version.parse(components.skip(1).join("-")),
             url: _serverFor(ref.description));
       }).where((id) => id != null).toList();
     } else {