fix: arm docker build failing on missing syscall

Update Qemu version.

.travis.yml

@@ -21,7 +21,7 @@ jobs:
     - 'echo "$DOCKER_PASSWORD" | docker login -u "$DOCKER_USERNAME" --password-stdin'
     - docker run --rm --privileged multiarch/qemu-user-static:register --reset
     - mkdir tmp
-    - "pushd tmp && curl -L -o qemu-arm-static.tar.gz https://github.com/multiarch/qemu-user-static/releases/download/v2.11.0/qemu-arm-static.tar.gz
+    - "pushd tmp && curl -L -o qemu-arm-static.tar.gz https://github.com/multiarch/qemu-user-static/releases/download/v4.2.0-6/qemu-arm-static.tar.gz
       && tar xzf qemu-arm-static.tar.gz && popd        \n"
     - docker build -f Dockerfile -t $REPO_BASE/signalk-server:linux-armhf-"$TRAVIS_BRANCH" --build-arg
       IMAGE_BASE=arm32v7/node .