Ignore case in regex in preprocessor

[bcroy]

tweetnlp/tweetnlp/util.py

Line 17 in 68b08c8

text = re.sub(r"@[A-Z,0-9]+", "@user", text)

For example, the text
"@realDonaldTrump and @KamalaHarris are running for president" is preprocessed to "@realDonaldTrump and @useramalaHarris are running for president"

This could be fixed by passing flags=re.IGNORECASE) to the re.sub call.