Pin release of the runtime dependencies in snap

This patch specifies the exact release of the dependencies to pull in,
this avoids regressions and incompatibilities from the new upstream
changes.

The maintainer should check and bump the dependency version once in a
while and check for breakage.
Signed-off-by: N林博仁(Buo-ren Lin) <Buo.Ren.Lin@gmail.com>

snap/snapcraft.yaml

@@ -34,6 +34,8 @@ parts:
   bottle:
     plugin: python
     source: https://github.com/bottlepy/bottle.git
+    source-branch: release-0.12
   docker:
     plugin: python
     source: https://github.com/docker/docker-py.git
+    source-tag: '3.7.0'