Show preview example in matrix

Author: Danny McCormick

README.md

@@ -30,7 +30,7 @@ jobs:
     runs-on: ubuntu-16.04
     strategy:
       matrix:
-        dotnet: [ '2.2.103', '3.5.2', '4.5.1' ]
+        dotnet: [ '2.2.103', '3.0.100-preview8-013656', '4.5.1' ]
     name: Dotnet ${{ matrix.dotnet }} sample
     steps:
       - uses: actions/checkout@master