Align assembly verions with package release 2.0.3

Current NuGet package release is at 2.0.3 (https://www.nuget.org/packages/ExCSS/2.0.3) but the assembly version attributes still reflect version 2.0.2.
Merge pull request #36 from atifaziz/patch-1

Align assembly verions with package release 2.0.3