fix broken example link in docs

The old way worked fine on my local server, but it gave me a 404
when I checked the production version on the RTD server. Hopefully
this will fix it?

adafruit_tlv320.py

@@ -87,7 +87,7 @@ For this one, the default headphone output volume will be way too low for
 use with a device that expects consumer line level input (-10 dBV). To fix
 that, you can increase ``dac_volume`` or ``headphone_volume``. If you want
 to experiment with different ways of setting the levels, check out the
-volume test example: `Volume test <../examples.html#volume-test>`_
+volume test example: `Volume test <./examples.html#volume-test>`_
 
 ::