ci: fix CI to use go1.16 (#128)

Also drop support for go1.14.

Author: myitcv

.github/workflows/test.yml

@@ -11,7 +11,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        go-version: [1.14.x, 1.15.x, 1.16.0-rc1]
+        go-version: [1.15.x, 1.16.x]
         os: [ubuntu-latest, macos-latest, windows-latest]
     runs-on: ${{ matrix.os }}
     steps: