fix goverals install

Author: umputun

.github/workflows/ci.yml

@@ -37,7 +37,7 @@ jobs:
 
       - name: install goveralls
         run: |
-          GO111MODULE=off go get -u -v github.com/mattn/goveralls
+          go install github.com/mattn/goveralls@latest
 
       - name: submit coverage
         run: $(go env GOPATH)/bin/goveralls -service="github" -coverprofile=$GITHUB_WORKSPACE/profile.cov