fix grammar for AggregateException.Flatten
fix grammar for AggregateException.Flatten

The old phrasing wasn't gramatically correct. It's somewhat
difficult to find a concise summary

alexperovich/coreclr,kyulee1/coreclr,sagood/coreclr,cshung/coreclr,dpodder/coreclr,mskvortsov/coreclr,JosephTremoulet/coreclr,sjsinju/coreclr,krk/coreclr,parjong/coreclr,qiudesong/coreclr,JosephTremoulet/coreclr,cydhaselton/coreclr,ragmani/coreclr,gkhanna79/coreclr,qiudesong/coreclr,AlexGhiondea/coreclr,cydhaselton/coreclr,James-Ko/coreclr,ruben-ayrapetyan/coreclr,JosephTremoulet/coreclr,qiudesong/coreclr,cshung/coreclr,yizhang82/coreclr,cydhaselton/coreclr,kyulee1/coreclr,kyulee1/coreclr,neurospeech/coreclr,sagood/coreclr,JosephTremoulet/coreclr,kyulee1/coreclr,cmckinsey/coreclr,gkhanna79/coreclr,parjong/coreclr,JonHanna/coreclr,cmckinsey/coreclr,russellhadley/coreclr,tijoytom/coreclr,cshung/coreclr,James-Ko/coreclr,gkhanna79/coreclr,sagood/coreclr,JonHanna/coreclr,dpodder/coreclr,yeaicc/coreclr,krk/coreclr,qiudesong/coreclr,pgavlin/coreclr,tijoytom/coreclr,cydhaselton/coreclr,mskvortsov/coreclr,cshung/coreclr,wateret/coreclr,dpodder/coreclr,sjsinju/coreclr,ruben-ayrapetyan/coreclr,rartemev/coreclr,poizan42/coreclr,cmckinsey/coreclr,mskvortsov/coreclr,poizan42/coreclr,James-Ko/coreclr,neurospeech/coreclr,dpodder/coreclr,russellhadley/coreclr,hseok-oh/coreclr,James-Ko/coreclr,mmitche/coreclr,rartemev/coreclr,wateret/coreclr,krk/coreclr,ruben-ayrapetyan/coreclr,alexperovich/coreclr,James-Ko/coreclr,krk/coreclr,YongseopKim/coreclr,wateret/coreclr,neurospeech/coreclr,alexperovich/coreclr,botaberg/coreclr,botaberg/coreclr,jamesqo/coreclr,sjsinju/coreclr,poizan42/coreclr,sjsinju/coreclr,russellhadley/coreclr,yeaicc/coreclr,hseok-oh/coreclr,hseok-oh/coreclr,wtgodbe/coreclr,sjsinju/coreclr,YongseopKim/coreclr,botaberg/coreclr,jamesqo/coreclr,rartemev/coreclr,AlexGhiondea/coreclr,cmckinsey/coreclr,wateret/coreclr,yizhang82/coreclr,YongseopKim/coreclr,cshung/coreclr,gkhanna79/coreclr,neurospeech/coreclr,cydhaselton/coreclr,yeaicc/coreclr,JonHanna/coreclr,sagood/coreclr,mmitche/coreclr,krytarowski/coreclr,rartemev/coreclr,krytarowski/coreclr,botaberg/coreclr,yeaicc/coreclr,krytarowski/coreclr,mmitche/coreclr,YongseopKim/coreclr,mmitche/coreclr,neurospeech/coreclr,JonHanna/coreclr,yeaicc/coreclr,yeaicc/coreclr,sjsinju/coreclr,wateret/coreclr,botaberg/coreclr,YongseopKim/coreclr,dpodder/coreclr,jamesqo/coreclr,ragmani/coreclr,mskvortsov/coreclr,krytarowski/coreclr,yizhang82/coreclr,parjong/coreclr,mskvortsov/coreclr,russellhadley/coreclr,dpodder/coreclr,yizhang82/coreclr,gkhanna79/coreclr,cmckinsey/coreclr,mmitche/coreclr,AlexGhiondea/coreclr,hseok-oh/coreclr,hseok-oh/coreclr,pgavlin/coreclr,alexperovich/coreclr,parjong/coreclr,sagood/coreclr,tijoytom/coreclr,ragmani/coreclr,AlexGhiondea/coreclr,wtgodbe/coreclr,JosephTremoulet/coreclr,poizan42/coreclr,YongseopKim/coreclr,pgavlin/coreclr,parjong/coreclr,krk/coreclr,ragmani/coreclr,tijoytom/coreclr,krytarowski/coreclr,wtgodbe/coreclr,rartemev/coreclr,AlexGhiondea/coreclr,cmckinsey/coreclr,krk/coreclr,JonHanna/coreclr,yeaicc/coreclr,AlexGhiondea/coreclr,rartemev/coreclr,pgavlin/coreclr,tijoytom/coreclr,JonHanna/coreclr,kyulee1/coreclr,ruben-ayrapetyan/coreclr,mskvortsov/coreclr,wateret/coreclr,jamesqo/coreclr,neurospeech/coreclr,alexperovich/coreclr,ruben-ayrapetyan/coreclr,mmitche/coreclr,gkhanna79/coreclr,pgavlin/coreclr,cshung/coreclr,parjong/coreclr,wtgodbe/coreclr,hseok-oh/coreclr,yizhang82/coreclr,cmckinsey/coreclr,qiudesong/coreclr,alexperovich/coreclr,JosephTremoulet/coreclr,botaberg/coreclr,poizan42/coreclr,yizhang82/coreclr,wtgodbe/coreclr,poizan42/coreclr,qiudesong/coreclr,tijoytom/coreclr,jamesqo/coreclr,russellhadley/coreclr,ragmani/coreclr,russellhadley/coreclr,kyulee1/coreclr,James-Ko/coreclr,ruben-ayrapetyan/coreclr,sagood/coreclr,krytarowski/coreclr,ragmani/coreclr,jamesqo/coreclr,wtgodbe/coreclr,cydhaselton/coreclr,pgavlin/coreclr