Upgrade protobuf to v3.5.1 (#1938)

* Upgrade protobuf to v3.5.1

* Update protobuf.rb

* Update protobuf.rb

Remove dependencies, since they are in chromebrew-core. Add "unzip" as dependency, because it is required to build the code

packages/protobuf.rb

@@ -3,17 +3,16 @@ require 'package'
 class Protobuf < Package
   description 'Protocol buffers are a language-neutral, platform-neutral extensible mechanism for serializing structured data.'
   homepage 'https://developers.google.com/protocol-buffers/'
-  version '3.3.0-2'
-  source_url 'https://github.com/google/protobuf/archive/v3.3.0.tar.gz'
-  source_sha256 '9a36bc1265fa83b8e818714c0d4f08b8cec97a1910de0754a321b11e66eb76de'
+  version '3.5.1'
+  source_url 'https://github.com/google/protobuf/archive/v3.5.1.tar.gz'
+  source_sha256 '826425182ee43990731217b917c5c3ea7190cfda141af4869e6d4ad9085a740f'
 
   binary_url ({
   })
   binary_sha256 ({
   })
 
-  depends_on 'automake' => :build
-  depends_on 'libtool'  => :build
+  depends_on 'unzip' => :build
 
   def self.build
     system './autogen.sh'