chore(examples): upgrade .NET Core example to NSpec.3.0.4-dev-27

Author: GiuseppePiscopo

examples/DotNetTestSample/test/LibrarySpecs/project.json

@@ -8,7 +8,7 @@
     "LibraryUnderTest": {
       "target": "project"
     },
-    "NSpec": "3.0.4",
+    "NSpec": "3.0.4-dev-27",
     "Shouldly": "2.8.2"
   },