fix cntk reference

Author: kMutagene

.gitignore

@@ -403,3 +403,4 @@ FodyWeavers.xsd
 /tmp/watch
 /.fsdocs
 /output
+src/BioFSharp.ML/Resources/dppop_test_results.tsv

src/BioFSharp.ML/BioFSharp.ML.fsproj

@@ -46,6 +46,6 @@
     <PackageReference Include="BioFSharp" Version="2.0.0" />
     <PackageReference Include="FSharpAux" Version="2.1.0" />
     <PackageReference Include="FSharpAux.IO" Version="2.1.0" />
-    <PackageReference Include="CNTK.CPUOnly" Version="2.8.0-rc0.dev20200201" />
+    <PackageReference Include="CNTK.CPUOnly" Version="2.7" />
   </ItemGroup>
 </Project>