Fix bug when commit session API endpoint returns 202 HTTP status code

[casperbrike]

Problem

Sometimes when we commit chunked uploads session Box API responds with 202 HTTP status code. In this case Box response is empty so parsed response is nil and we get an error when we try to read from parsed response:

https://github.com/casperbrike/boxr/blob/f71a97ba8f79bffb3bd3c36defb945ac17d8e081/lib/boxr/chunked_uploads.rb#L196-L198

Tech changes

• Added a method with_retry_on_202 that yields a block (expecting that a call to Box API will passed in a block), checks response status, if it's 202 then sleeps for value specified in retry-after response header (as Box' documentation recommends): https://developer.box.com/guides/uploads/chunked/commit-session/
• Wrapped commit chunked upload session API call into with_retry_on_202