fix(content): DebuggerShim is missing NSpec.Assertions import

Fixes #172

Author: GiuseppePiscopo

sln/content/DebuggerShim.cs

@@ -1,6 +1,7 @@
 using System.Linq;
 using System.Reflection;
 using NSpec;
+using NSpec.Assertions;
 using NSpec.Domain;
 using NSpec.Domain.Formatters;