Update snapcraft docker image contain snapcraft 2.42.1

ci/docker-snapcraft/Dockerfile

@@ -0,0 +1,7 @@
+FROM snapcraft/xenial-amd64
+
+# Update snapcraft to latest version
+RUN apt-get update -qq \
+ && apt-get install -y snapcraft \
+ && rm -rf /var/lib/apt/lists/* \
+ && snapcraft --version

ci/docker-snapcraft/build.sh

@@ -0,0 +1,6 @@
+#!/bin/bash -ex
+
+cd "$(dirname "$0")"
+
+docker build -t solanalabs/snapcraft .
+docker push solanalabs/snapcraft