Replace deprecated request_fingerprint with fingerprint in cache and dupefilter files

[DharmeshPandav]

request_fingerprint is deprecated in scrapy 2.7 and is replaced by fingerprint,

Using request_fingerprint results in deprecation warning in logs

https://docs.scrapy.org/en/latest/topics/request-response.html#std-setting-REQUEST_FINGERPRINTER_IMPLEMENTATION

scrapy-splash/scrapy_splash/cache.py

Line 13 in 6a9eb9c

from .dupefilter import splash_request_fingerprint

scrapy-splash/scrapy_splash/dupefilter.py

Line 20 in 6a9eb9c

fp = request_fingerprint(request, include_headers=include_headers)

scrapy-splash/scrapy_splash/__init__.py

Line 10 in 6a9eb9c

from .dupefilter import SplashAwareDupeFilter, splash_request_fingerprint