snap: use master branch to test the snap

Use master branch to test the snap in order to detect errors earlier
before releasing the next snap

fixes #663

Signed-off-by: Julio Montes <julio.montes@intel.com>

snap/snapcraft.yaml

@@ -1,5 +1,5 @@
 name: kata-containers
-version: "1.9.0-alpha0"
+version: "master"
 summary: Build lightweight VMs that seamlessly plug into the containers ecosystem
 description: |
   Kata Containers is an open source project and community working to build a