Lemmas of pluralized numerals that are multiples of 10 (e.g. decade-years)

[nschneid]

These should be changed to follow GUM and keep "s" (but not apostrophe) in the lemma, as discussed at amir-zeldes/gum#169

E.g., "1970s" or "1970's" would have "1970s" as the lemma. (These are tagged NOUN/NNS, not NUM.)

EWT tokens:

• [x] 39 with just digits in the lemma
• [x] 5 with a prefix plus digits (1 false positive)
• [x] "Sixties", "eighties", "mid-nineties" per this query