ci: include upcoming go1.16 in build matrix

Author: pjvds

.github/workflows/test.yml

@@ -11,7 +11,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        go-version: [1.14.x, 1.15.x]
+        go-version: [1.14.x, 1.15.x, go1.16.0-beta1]
         os: [ubuntu-latest, macos-latest, windows-latest]
     runs-on: ${{ matrix.os }}
     steps: