trim leaving version prefix in tag

.travis.yml

@@ -17,6 +17,7 @@ after_success:
   - echo "$DOCKER_PASSWORD" | docker login -u "$DOCKER_USERNAME" --password-stdin
   - docker push "sixtlabs/gomodproxy:latest"
   - if [ ! -z $TRAVIS_TAG ] ; then
-      docker tag sixtlabs/gomodproxy:latest sixtlabs/gomodproxy:$TRAVIS_TAG;
-      docker push sixtlabs/gomodproxy:$TRAVIS_TAG;
+      TAG=$(echo $TRAVIS_TAG | sed 's/^v//');
+      docker tag sixtlabs/gomodproxy:latest sixtlabs/gomodproxy:$TAG;
+      docker push sixtlabs/gomodproxy:$TAG;
     fi