Fix typo in README
Fix typo in README

JanSchulz/IRkernel,chendaniely/IRkernel,ibm-et/IRkernel,ibm-et/IRkernel,gdtm86/IRkernel,ChinaQuants/IRkernel,elaOnMars/IRkernel,Phobia0ptik/IRkernel,rgbkrk/IRkernel,mikecroucher/IRkernel