Prism highlighting does not update all lines when changing syntax

[echenley]

This probably has something to do with the lines refactor: #10. The more basic Slate code-highlighting example does not have this issue: http://slatejs.org/#/code-highlighting

Steps to Reproduce

• open a document on gitbook.com
• make a code block with

var line1;
var line2;

• change syntax to javascript, then to css
• only currently focused line is updated
• if you focus the beginning of the incorrectly highlighted line, it triggers prism to update it
• if you focus the end of the incorrectly highlighted line, it throws an error

[Soreine]

Fixed in GitbookIO/slate-prism#5