fix(install): Fix invalid reference format again (#231)

Fix #230.

install.sh

@@ -1,6 +1,8 @@
 #!/usr/bin/env bash
 set -e
 
+LATEST_STABLE_SENTRY_IMAGE='sentry:9.1.2'
+
 MIN_DOCKER_VERSION='17.05.0'
 MIN_COMPOSE_VERSION='1.17.0'
 MIN_RAM=3072 # MB
@@ -55,6 +57,12 @@ else
   cp -n .env.example "$ENV_FILE"
 fi
 
+if [ -z $SENTRY_IMAGE ]; then
+  echo ""
+  echo "\$SENTRY_IMAGE not set, using latest stable: $LATEST_STABLE_SENTRY_IMAGE";
+  export SENTRY_IMAGE=$LATEST_STABLE_SENTRY_IMAGE
+fi
+
 echo ""
 echo "Building and tagging Docker images..."
 echo ""