pubspec: Shorten package description

Author: nebkat

pubspec.yaml

@@ -1,6 +1,6 @@
 name: physical
 version: 0.5.1
-description: A lightweight Dart library for dealing with physical quantities, units, and conversions.
+description: Lightweight library for dealing with physical quantities, units, and conversions.
 homepage: https://github.com/nebkat/dart-physical
 repository: https://github.com/nebkat/dart-physical
 documentation: https://github.com/nebkat/dart-physical/blob/master/README.md