Use exact format for parsing `StarSign`.

[drasmart]

Changes

• Replace DateTime.Parse calls with DateTime.ParseExact.

Why

• The Example throws at different system locale settings:

  Exception thrown: 'System.FormatException' in System.Private.CoreLib.dll
  An exception of type 'System.FormatException' occurred in System.Private.CoreLib.dll but was not handled in user code
  String '21/03' was not recognized as a valid DateTime.