Replace temfile.SpooledTemporaryFile with tempfile.NamedTemporaryFile (#870)
Replace temfile.SpooledTemporaryFile with tempfile.NamedTemporaryFile (#870)

* Replace `tempfile.SpooledTemporaryFile` with `tempfile.NamedTemporaryFile` in exports code
* Closes #869 
ajvpot/CTFd,LosFuzzys/CTFd,isislab/CTFd,LosFuzzys/CTFd,isislab/CTFd,ajvpot/CTFd,isislab/CTFd,LosFuzzys/CTFd,ajvpot/CTFd,CTFd/CTFd,isislab/CTFd,CTFd/CTFd,CTFd/CTFd,ajvpot/CTFd,CTFd/CTFd,LosFuzzys/CTFd