replace function into arrow function in README

Author: oprogramador

Diff for: README.md

@@ -20,9 +20,7 @@ fs.createReadStream('ex.txt')
     callback()
    }))
   .pipe(fs.createWriteStream('out.txt'))
-  .on('finish', function () {
-    doSomethingSpecial()
-  })
+  .on('finish', () => doSomethingSpecial())
 ```
 
 Or object streams:
@@ -42,10 +40,10 @@ fs.createReadStream('data.csv')
 
     callback()
   }))
-  .on('data', function (data) {
+  .on('data', (data) => {
     all.push(data)
   })
-  .on('end', function () {
+  .on('end', () => {
     doSomethingSpecial(all)
   })
 ```
@@ -67,7 +65,7 @@ The `options` argument is first, unlike standard convention, because if I'm pass
 ```js
 fs.createReadStream('/tmp/important.dat')
   .pipe(through2({ objectMode: true, allowHalfOpen: false },
-    function (chunk, enc, cb) {
+    (chunk, enc, cb) => {
       cb(null, 'wut?') // note we can use the second argument on the callback
                        // to provide data as an alternative to this.push('wut?')
     }
@@ -92,7 +90,7 @@ The optional `flushFunction` is provided as the last argument (2nd or 3rd, depen
 ```js
 fs.createReadStream('/tmp/important.dat')
   .pipe(through2(
-    function (chunk, enc, cb) { cb(null, chunk) }, // transform is a noop
+    (chunk, enc, cb) => cb(null, chunk), // transform is a noop
     function (cb) { // flush function
       this.push('tacking on an extra buffer to the end');
       cb();