.travis.yml Fix another missing snapcraft:stable

Author: abitrolly

.travis.yml

@@ -26,7 +26,7 @@ jobs:
     env: EMPTY
     before_install: skip
     install: skip
-    script: docker run -v $(pwd):$(pwd) -w $(pwd) snapcore/snapcraft snapcraft
+    script: docker run -v $(pwd):$(pwd) -w $(pwd) snapcore/snapcraft:stable snapcraft
 after_success:
 - openssl aes-256-cbc -K $encrypted_8b01c2e263fa_key -iv $encrypted_8b01c2e263fa_iv
   -in .snapcraft/travis_snapcraft.cfg -out .snapcraft/snapcraft.cfg -d