Use node-nsspellchecker to replace $native's spell checker.

src/packages/spell-check/lib/misspelling-view.coffee

@@ -1,6 +1,7 @@
 {View} = require 'space-pen'
 Range = require 'range'
 CorrectionsView = require './corrections-view'
+NSSpellChecker = require 'nsspellchecker'
 
 module.exports =
 class MisspellingView extends View
@@ -30,7 +31,7 @@ class MisspellingView extends View
 
       screenRange = @getScreenRange()
       misspelling = @editor.getTextInRange(@editor.bufferRangeForScreenRange(screenRange))
-      corrections = $native.getCorrectionsForMisspelling(misspelling)
+      corrections = NSSpellChecker.getCorrectionsForMisspelling(misspelling)
       @correctionsView?.remove()
       @correctionsView = new CorrectionsView(@editor, corrections, screenRange)
 

src/packages/spell-check/lib/spell-check-handler.coffee

@@ -1,3 +1,5 @@
+NSSpellChecker = require 'nsspellchecker'
+
 module.exports =
   findMisspellings: (text) ->
     wordRegex = /(?:^|[\s\[\]])([a-zA-Z']+)(?=[\s\.\[\]]|$)/g
@@ -6,7 +8,7 @@ module.exports =
     for line in text.split('\n')
       while matches = wordRegex.exec(line)
         word = matches[1]
-        continue unless $native.isMisspelled(word)
+        continue unless NSSpellChecker.isMisspelled(word)
         startColumn = matches.index + matches[0].length - word.length
         endColumn = startColumn + word.length
         misspellings.push([[row, startColumn], [row, endColumn]])