Resolve "Add an "update framework and dependencies" script"

Closes #27 (closed)

upgrade.sh

+#!/usr/bin/env bash
+
+set -o errexit
+set -o nounset
+set -o pipefail
+
+# Check dependencies
+command -v flutter >/dev/null 2>&1 || {
+  echo >&2 "I require flutter but it's not installed. Aborting."
+  exit 1
+}
+
+flutter pub upgrade
+flutter pub upgrade --major-versions
+flutter pub get
+
+flutter build apk --debug