Install latest stable version of Juju

Revert a previous commit to pin Juju releases to 2.5 branch. The issue that led to that has since been fixed.

Change-Id: I19522c4efcb154b6e80bbf4427ba8021386a91ee
Signed-off-by: Adam Israel <adam.israel@canonical.com>
diff --git a/installers/full_install_osm.sh b/installers/full_install_osm.sh
index 48f2cae..1e86fbd 100755
--- a/installers/full_install_osm.sh
+++ b/installers/full_install_osm.sh
@@ -631,7 +631,7 @@
 
 function install_juju() {
     echo "Installing juju"
-    sudo snap install juju --classic --channel=2.5/stable
+    sudo snap install juju --classic
     [ -z "$INSTALL_NOLXD" ] && sudo dpkg-reconfigure -p medium lxd
     echo "Finished installation of juju"
     return 0