Undo bad edit.

pkgs/package_config/lib/src/errors.dart

diff --git a/pkgs/package_config/lib/src/errors.dart b/pkgs/package_config/lib/src/errors.dart
index f60a2dc..0fc77bb 100644
--- a/pkgs/package_config/lib/src/errors.dart
+++ b/pkgs/package_config/lib/src/errors.dart
@@ -29,7 +29,7 @@
      implements PackageConfigError {
 
   new from(FormatException exception)
-    : this(exception.message, exception.source, exception.offset);
+    : super.value(exception.message, exception.source, exception.offset);
 }
 
 /// The default `onError` handler.