fix scrollToBottom() version check for jQuery > 1.10

jQuery uses a form of [semantic versioning][semver], where 1.9 < 1.10
< 1.11. The old scrollToBottom() version check used lexicographic
ordering, which doesn't work with the newest jQuery, since "1.10" <
"1.6". This commit changes that check to extract each component, parse
them into an int, and then compare.

 [semver]: http://semver.org/