Update _piwik.html.haml

Created by: r00t0vi4

Matomo core developers are recommended to use "js/" instead of "piwik.js" and "piwik.php":

• js/index.php (or implicitly as "js/") can be used to serve up the minified piwik.js;
• it supports conditional-GET and Last-Modified, so piwik.js can be cached by the browser;
• it supports deflate/gzip compression if your web server (e.g., Apache without mod_deflate or mod_gzip), shrinking the data transfer to 8K;
• js/index.php (or implicitly as "js/") can also act as a proxy to piwik.php;
• If you are concerned about the impact of browser-based privacy filters which attempt to block tracking, you can change your tracking code to use "js/" instead of "piwik.js" and "piwik.php", respectively.

https://github.com/matomo-org/matomo/blob/3.x-dev/js/README.md

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