snap: Update snap config.

Updating the config as suggested by the snap community here - 
https://forum.snapcraft.io/t/snap-fails-to-load-error-minidump-segmentation-fault/8691/5

Should improve #593.

snap/snapcraft.yaml

@@ -1,5 +1,5 @@
 name: zulip
-version: 2.0.0
+version: 2.3.82
 summary: Zulip Desktop Client for Linux
 description: Zulip combines the immediacy of Slack with an email threading model. With Zulip, you can catch up on important conversations while ignoring irrelevant ones.
 confinement: strict
@@ -34,4 +34,4 @@ parts:
       - libxtst6
     source: dist/linux-unpacked
     after:
-      - desktop-gtk2
+      - desktop-gtk3