Add go1.18 to the test matrix

Github actions support go1.18 as well

Author: moredure

.github/workflows/ci.yml

@@ -5,7 +5,7 @@ jobs:
  test:
  strategy:
  matrix:
- go: [ 1.17, 1.16, 1.15 ]
+ go: [ 1.18, 1.17, 1.16, 1.15 ]
  name: Tests Go ${{ matrix.go }}
  runs-on: ubuntu-18.04