fix(ci): update coverage workflow

Author: aymanbagabas

.github/workflows/coverage.yml

@@ -24,5 +24,5 @@ jobs:
           COVERALLS_TOKEN: ${{ secrets.GITHUB_TOKEN }}
         run: |
           go test -race -covermode atomic -coverprofile=profile.cov ./...
-          GO111MODULE=off go get github.com/mattn/goveralls
-          $(go env GOPATH)/bin/goveralls -coverprofile=profile.cov -service=github
+          go install github.com/mattn/goveralls@latest
+          goveralls -coverprofile=profile.cov -service=github