docs: Update link to Tao of tmux book

Author: tony

docs/_templates/book.html

@@ -4,4 +4,4 @@ <h3>The book!</h3>
 
 <p><em>The Tao of tmux</em> is available on <a class="reference external" href="https://leanpub.com/the-tao-of-tmux" rel="noopener noreferrer" target="_blank">Leanpub</a> and <a class="reference external" href="http://amzn.to/2gPfRhC" rel="noopener noreferrer" target="_blank">Kindle</a> (Amazon).</p>
 <p>Read and browse the book for <a class="reference external" href="https://leanpub.com/the-tao-of-tmux/read" rel="noopener noreferrer" target="_blank">free on the web</a>.</p>
-<a class="reference external image-reference" href="http://amzn.to/2gPfRhC" rel="noopener noreferrer" target="_blank"><img alt="Amazon Kindle" src="https://www.git-pull.com/_images/amazon-logo.png" width="45%"></a>
+<a class="reference external image-reference" href="http://amzn.to/2gPfRhC" rel="noopener noreferrer" target="_blank"><img alt="Amazon Kindle" src="https://tony.sh/_images/amazon-logo.png" width="45%"></a>