Improve example codes snippets
Most of java example has some sort of error in them. I.e on sandbox api select page, https://app.mailgun.com/app/sending/domains/sandboxeacdf7ff738d4717b892e9991128d26f.mailgun.org, example has an extra comman. While its not a big deal, having experience the quality of doc from AWS and Google, this type of untested code snippets really irritates users. Hope you guys go though your example codes and test them before posting.