- updated to version 1.6.8

==== Features

Several changes were made to improve performance:

* [MRI] Simplify NodeSet#to_a with a minor speed-up. (#1397)
* XML::Node#ancestors optimization. (#1297) (Thanks, Bruno Sutic!)
* Use Symbol#to_proc where we weren't previously. (#1296) (Thanks, Bruno Sutic!)
* XML::DTD#each uses implicit block calls. (Thanks, @glaucocustodio!)
* Fall back to the `pkg-config` gem if we're having trouble finding the system libxml2. This should help many FreeBSD users. (#1417)
* Set document encoding appropriately even on blank document. (#1043) (Thanks, @batter!)

==== Bug Fixes

* [JRuby] fix slow add_child (#692)
* [JRuby] fix load errors when deploying to JRuby/Torquebox (#1114) (Thanks, @atambo and @jvshahid!)
* [JRuby] fix NPE when inspecting nodes returned by NodeSet#drop (#1042) (Thanks, @mkristian!)
* [JRuby] fix nil attriubte node's namespace in reader (#1327) (Thanks, @codekitchen!)
* [JRuby] fix Nokogiri munging unicode characters that require more than 2 bytes (#1113) (Thanks, @mkristian!)
* [JRuby] allow unlinking an unparented node (#1112, #1152) (Thanks, @esse!)
* [JRuby] allow Fragment parsing on a frozen string (#444, #1077)
* [JRuby] HTML `style` tags are no longer encoded (#1316) (Thanks, @tbeauvais!)
* [MRI] fix assertion failure while accessing attribute node's namespace in reader (#843) (Thanks, @2potatocakes!)
* [MRI] fix issue with GCing namespace nodes returned in an xpath query. (#1155)
* [MRI] Ensure C strings are null-terminated. (#1381)
* [MRI] Ensure Rubygems is loaded before using mini_portile2 at installation. (#1393, #1411) (Thanks, @JonRowe!)
* [MRI] Handling another edge case where the `libxml-ruby` gem's global callbacks were smashing the heap. (#1426). (Thanks to @bbergstrom for providing an isolated test case!)
* [MRI] Ensure encodings are passed to Sax::Parser xmldecl callback. (#844)
* [MRI] Ensure default ns prefix is applied correctly when reparenting nodes to another document. (#391) (Thanks, @ylecuyer!)