memory leak for URLSession

[Shvier]

• Platform: iOS x86 Simulator
• OS Version: 13.3
• Issue Detail
  class HTTP in AcceptSDK does not deallocate after getTokenWithRequest completed

• Steps to Reproduce
  call getTokenWithRequest

• Reason
  In this line, class HTTP has been set as URLSession's delegate, and URLSessionDelegate is a strong reference property, not weak reference

• Solution
  After task has finished, making URLSession invalidate will remove the reference to HTTP.
  session.finishTasksAndInvalidate()
  Add the above code after semaphore.wait