Rename Tempo => Changes (#2087)

## Changes

<!-- List the changes this PR makes. -->

- Rename Tempo => Changes
- Update the screenshot

## Context

<!-- Explain why you're making these changes. -->

I changed the app’s name as part of the latest version upgrade, so I’d
appreciate it if you could update it.

Author: dscho

data/guis/changes.yml

@@ -0,0 +1,11 @@
+---
+name: "Changes"
+project_url: "https://github.com/maoyama/Changes"
+image_tag: "images/guis/changes@2x.png"
+platforms:
+  - "Mac"
+price: "Free"
+license: "MIT"
+trend_name: "changes"
+order: 60
+---