travis: try using codecov (#131)

internal/runtests.sh

@@ -29,6 +29,7 @@ if [[ "$TRAVIS_OS_NAME" == "linux" ]]; then
   go test -race -coverpkg=./... -coverprofile=coverage.out ./... || result=1
   if [ -f coverage.out ]; then
     goveralls -coverprofile=coverage.out -service=travis-ci
+    bash <(curl -s https://codecov.io/bash)
   fi
   # Ensure that the code has no extra dependencies (including transitive
   # dependencies) that we're not already aware of by comparing with