I have used okhttp and It\'s working fine with following dependency:
compile \'com.squareup.okhttp:okhttp:2.3.0\'
Recently
It is called MultipartBody.Builder now. From the ChangeLog:
Form and Multipart bodies are now modeled. We've replaced the opaque FormEncodingBuilder with the more powerful FormBody and FormBody.Builder combo. Similarly we've upgraded MultipartBuilder into MultipartBody, MultipartBody.Part, and MultipartBody.Builder.
You can read more here.