Use writeFile instead of gm write

lib/args.js

@@ -5,6 +5,7 @@
 var argsToArray = require('./utils').argsToArray;
 var isUtil = require('./utils').isUtil;
 var tmp = require('tmp');
+var fs = require('fs');
 /**
  * Extend proto
  */
@@ -108,22 +109,13 @@ module.exports = function (proto) {
     function appendBuffer(self, buf) {
       if (buf.byteLength <= 0)
         return false;
-      
-      
-      var m = {
-        '_options': self._options, 
-        'source': buf, 
-        'sourceBuffer': buf
-      };
 
       var tmpFileName = tmp.tmpNameSync();
       
-      var args = ['convert', '-', tmpFileName];
-
       self._append.push(tmpFileName);
       
       self.preprocessor(function (callback) {
-        self._spawn.call(m, args, true, callback);
+        fs.writeFile(tmpFileName, buf, callback);
       });
       
       return true;