Change mbstring requirement to a suggestion
Change mbstring requirement to a suggestion

thephpleague/commonmark,stof/commonmark,thephpleague/commonmark,fesor/commonmark,kkiernan/commonmark,hason/commonmark,colinodell/commonmark,garethellis36/commonmark,bcremer/commonmark,kkiernan/commonmark,postalservice14/commonmark,hason/commonmark,postalservice14/commonmark,fesor/commonmark,garethellis36/commonmark