Use the built-in zlib module instead of iltorb

As the latter has been deprecated:
nstepien/iltorb#119 (comment)

index.js

@@ -3,7 +3,7 @@ var RSVP = require('rsvp'),
     helpers = require('broccoli-kitchen-sink-helpers'),
     Filter = require('broccoli-filter'),
     Buffer = require('buffer').Buffer,
-    brotli = require('iltorb');
+    zlib = require('zlib');
 
 
 BrotliFilter.prototype = Object.create(Filter.prototype);
@@ -21,14 +21,7 @@ function BrotliFilter(inputNode, options) {
     if (!(this instanceof BrotliFilter))
         return new BrotliFilter(inputNode, options);
 
-    options = options || {};
-
-    this.brotliOptions = {
-        mode: options.mode || 0,
-        quality: options.quality || 11,
-        lgwin: options.lgwin || 22,
-        lgblock: options.lgblock || 0
-    };
+    this.brotliOptions = options || {};
     this.keepUncompressed = options.keepUncompressed;
     this.appendSuffix = (options.hasOwnProperty('appendSuffix') ?
                          options.appendSuffix :
@@ -55,7 +48,7 @@ BrotliFilter.prototype.processFile = function(srcDir, destDir, relativePath) {
 };
 
 BrotliFilter.prototype.processString = function(str) {
-    return RSVP.denodeify(brotli.compress)(Buffer.from(str), this.brotliOptions);
+    return RSVP.denodeify(zlib.brotliCompress)(Buffer.from(str), this.brotliOptions);
 };
 
 BrotliFilter.prototype.getDestFilePath = function() {

package.json

@@ -24,7 +24,6 @@
   "dependencies": {
     "broccoli-filter": "^1.2.4",
     "broccoli-kitchen-sink-helpers": "^0.3.1",
-    "iltorb": "^2.0.2",
     "rsvp": "^4.7.0"
   }
 }

tests/index.js

@@ -1,7 +1,7 @@
 var brotli = require('../index');
 
 var RSVP = require('rsvp');
-var iltorb = require('iltorb');
+var zlib = require('zlib');
 var expect = require('expect.js');
 
 var fs = require('fs');
@@ -32,7 +32,7 @@ describe('broccoli-brotli', function(){
             return RSVP.hash({
                 dir: builder.outputPath,
                 actualCsv: fs.readFileSync(sourcePath + '/test.csv'),
-                actualText: RSVP.denodeify(iltorb.decompress)(brotledText)
+                actualText: RSVP.denodeify(zlib.brotliDecompress)(brotledText)
             });
         }).then(function(result) {
             expect(result.actualText).to.eql(textContent);
@@ -54,7 +54,7 @@ describe('broccoli-brotli', function(){
             return RSVP.hash({
                 dir: builder.outputPath,
                 actualCsv: fs.readFileSync(builder.outputPath + '/test.csv'),
-                actualText: RSVP.denodeify(iltorb.decompress)(brotledText)
+                actualText: RSVP.denodeify(zlib.brotliDecompress)(brotledText)
             });
         }).then(function(result) {
             expect(result.actualText).to.eql(textContent);
@@ -75,7 +75,7 @@ describe('broccoli-brotli', function(){
             var brotledText = fs.readFileSync(builder.outputPath + '/test.txt');
             return RSVP.hash({
                 dir: builder.outputPath,
-                actualText: RSVP.denodeify(iltorb.decompress)(brotledText)
+                actualText: RSVP.denodeify(zlib.brotliDecompress)(brotledText)
             });
         }).then(function(result) {
             expect(result.actualText).to.eql(textContent);