Upgrade to Uploadcare API 0.7

[sbailliez]

Describe the bug

Client requests are being sent as 0.6 while other libraries like Ruby are using 0.7, The Uploadcare server returns a warning to use 0.7 in the headers.

The java client should be updated to support the latest version.

Expected behavior

Supports 0.7

Code / screenshots

Version 0.6 is currently sent in the request

uploadcare-java/src/main/java/com/uploadcare/api/RequestHelper.java

Line 120 in a7bc483

request.setHeader("Accept", "application/vnd.uploadcare-v0.6+json");

Some model changes might be needed to support 0.7

Environment

N/A