I changed ruby-doc.org to offer up the 1.8.6 docs by default. My
understanding is that there are far more people sticking with 1.8.6
(such as myself) instead of moving to 1.8.7, so making 1.8.6 the default
is less confusing.
The 1.8.7 docs are still there, though (but not for std-lib; I need to
work out a nicer way to gen those docs for different source paths so as
to offer multiple versions).
There’s a link for that on the main ruby-doc.org page