change default token_pattern in Vectorizer class

Hey,
I suggest changing default token_pattern in Vectorizer class to exclude any words start with numerical number.
Usually those are meaningless numbers and should be treated as noise in text mining.

For example, when I run "topics_extraction_with_nmf" script, I got a weird topic with top words
"10" "00" "space" "new" "11" "12" "15".....

Thanks!