Wrong `Accept` header field value in DeliveryClient.buildNewRequest()

[Dakkaron]

Brief bug description

Requests are sent with header Accept set to applications/json instead of application/json.

Repro steps

1. Send a request e.g. using DeliveryClient.getItem().
2. Observe the headers of the sent request.
3. It is applications/json.

Expected behavior

Accept header should be set to application/json.

Test environment

• Platform/OS: Java, Windows
• Browser: N/A
• Version: Current master branch

Additional context

The problem derives from https://github.com/kontent-ai/java-packages/blob/master/delivery-sdk/src/main/java/kontent/ai/delivery/DeliveryClient.java, line 587.

[IvanKiral]

Hey, I created a PR #155 can you check it out?

[Dakkaron]

Nice, thanks a lot, looks great!

[IvanKiral]

Should be released in 5.1.2 :)