Build cross binary only on tags in travis

.travis.yml

@@ -1,6 +1,9 @@
 sudo: required
 dist: trusty
 
+git:
+  depth: false
+
 services:
   - docker
 
@@ -21,12 +24,13 @@ before_deploy:
       sudo -E apt-get -yq update;
       sudo -E apt-get -yq --no-install-suggests --no-install-recommends --force-yes install docker-ce=${DOCKER_VERSION}*;
       docker version;
-      make -j${N_MAKE_JOBS} crossbinary-parallel;
-      make image-dirty;
+      if [ "$TRAVIS_TAG" ]; then
+        make -j${N_MAKE_JOBS} crossbinary-parallel;
+        make image-dirty;
+      fi;
       curl -sI https://github.com/containous/structor/releases/latest | grep -Fi Location  | tr -d '\r' | sed "s/tag/download/g" | awk -F " " '{ print $2 "/structor_linux-amd64"}' | wget --output-document=$GOPATH/bin/structor -i -;
       chmod +x $GOPATH/bin/structor;
       structor -o containous -r traefik --dockerfile-url="https://raw.githubusercontent.com/containous/traefik/master/docs.Dockerfile" --menu.js-url="https://raw.githubusercontent.com/containous/structor/master/traefik-menu.js.gotmpl" --exp-branch=master --debug;
-      tar cfz dist/traefik-${VERSION}.src.tar.gz --exclude-vcs --exclude dist .;
     fi
 deploy:
   - provider: releases
@@ -56,4 +60,3 @@ deploy:
     on:
       repo: containous/traefik
       all_branches: true
-