Use _.isArray to determine whether a value is Array.

When passing arrays between child processes with node's IPC machanism,
`instance of Array` will return false for the deserialized array, we
should use the reiable way of detecting Array provided by underscore.

Read this for more:
http://perfectionkills.com/instanceof-considered-harmful-or-how-to-write-a-robust-isarray/

This bug was found when moving spell-check to use ProcessTask, and the
wrong Range object was returned for the passed misspelling value.

src/app/point.coffee

@@ -1,10 +1,12 @@
+_ = require 'underscore'
+
 module.exports =
 class Point
   @fromObject: (object) ->
     if object instanceof Point
       object
     else
-      if object instanceof Array
+      if _.isArray(object)
         [row, column] = object
       else
         { row, column } = object

src/app/range.coffee

@@ -31,7 +31,7 @@ class Range
     new Range(@start.copy(), @end.copy())
 
   isEqual: (other) ->
-    if other instanceof Array and other.length == 2
+    if _.isArray(other) and other.length == 2
       other = new Range(other...)
 
     other.start.isEqual(@start) and other.end.isEqual(@end)