Fix undeclared var warnings in CLJS

[jkrasnay]

Version 0.6.6 generates the following warnings when compiling for CLJS:

------ WARNING #1 - :undeclared-var --------------------------------------------
 Resource: editscript/diff/a_star.cljc:54:16
 Use of undeclared Var editscript.diff.a-star/Node
--------------------------------------------------------------------------------

------ WARNING #2 - :undeclared-var --------------------------------------------
 Resource: editscript/diff/a_star.cljc:55:16
 Use of undeclared Var editscript.diff.a-star/Node
--------------------------------------------------------------------------------

Unfortunately this broke my build as I have configured undeclared var warnings to be reported as errors.

I think this could be easily fixed by importing editscript.util.index/Node for both CLJ and CLJS.

[huahaiy]

PR welcome