Slate: backspacing to the start of an inline node errors

[ianstormtaylor]

From #317:

Inserting a link at the start of a line, and then backspacing from the end of the link to its beginning: as the first character is deleted it throws Uncaught Error: Could not find a descendant node with key "xinw".

[joelburget]

I'd like this fixed and could take a look, but would prefer guidance on how you'd tackle it first.

[aeneasr]

This is resolved in the 0.15 branch!

[ianstormtaylor]

Woot!