DOC: pdoc template: Specify rel=canonical w/o index.html

doc/pdoc_template/head.mako

@@ -25,5 +25,5 @@

<style>${homelink()}</style>
<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/highlight.js/9.12.0/styles/github.min.css">
<link rel="canonical" href="https://kernc.github.io/backtesting.py/doc/${module.url(link_prefix=link_prefix)}">
<link rel="canonical" href="https://kernc.github.io/backtesting.py/doc/${module.url()[:-len('index.html')] if module.is_package else module.url()}">
<link rel="icon" href="https://kernc.github.io/backtesting.py/logo.png">