Update swiper.d.ts
Update swiper.d.ts

Latest SwiperOptions also has `prevButton` and `nextButton` as optional strings.
pocesar/DefinitelyTyped,micurs/DefinitelyTyped,abner/DefinitelyTyped,borisyankov/DefinitelyTyped,AgentME/DefinitelyTyped,alexdresko/DefinitelyTyped,ashwinr/DefinitelyTyped,pocesar/DefinitelyTyped,AbraaoAlves/DefinitelyTyped,QuatroCode/DefinitelyTyped,arusakov/DefinitelyTyped,scriby/DefinitelyTyped,martinduparc/DefinitelyTyped,smrq/DefinitelyTyped,hellopao/DefinitelyTyped,nycdotnet/DefinitelyTyped,shlomiassaf/DefinitelyTyped,DzmitryDulko/DefinitelyTyped,georgemarshall/DefinitelyTyped,QuatroCode/DefinitelyTyped,yuit/DefinitelyTyped,slavomirvojacek/adbrain-typescript-definitions,syuilo/DefinitelyTyped,ashwinr/DefinitelyTyped,DzmitryDulko/DefinitelyTyped,mattblang/DefinitelyTyped,zuzusik/DefinitelyTyped,rcchen/DefinitelyTyped,xStrom/DefinitelyTyped,newclear/DefinitelyTyped,schmuli/DefinitelyTyped,GiedriusGrabauskas/DefinitelyTyped,hellopao/DefinitelyTyped,danfma/DefinitelyTyped,danfma/DefinitelyTyped,mattblang/DefinitelyTyped,amanmahajan7/DefinitelyTyped,arusakov/DefinitelyTyped,rolandzwaga/DefinitelyTyped,dsebastien/DefinitelyTyped,jraymakers/DefinitelyTyped,gandjustas/DefinitelyTyped,alvarorahul/DefinitelyTyped,use-strict/DefinitelyTyped,slavomirvojacek/DefinitelyTyped,georgemarshall/DefinitelyTyped,markogresak/DefinitelyTyped,benliddicott/DefinitelyTyped,rolandzwaga/DefinitelyTyped,aciccarello/DefinitelyTyped,nainslie/DefinitelyTyped,subash-a/DefinitelyTyped,psnider/DefinitelyTyped,alvarorahul/DefinitelyTyped,mcliment/DefinitelyTyped,Penryn/DefinitelyTyped,damianog/DefinitelyTyped,georgemarshall/DefinitelyTyped,progre/DefinitelyTyped,subash-a/DefinitelyTyped,schmuli/DefinitelyTyped,psnider/DefinitelyTyped,laurentiustamate94/DefinitelyTyped,zuzusik/DefinitelyTyped,slavomirvojacek/adbrain-typescript-definitions,chrootsu/DefinitelyTyped,smrq/DefinitelyTyped,donnut/DefinitelyTyped,AgentME/DefinitelyTyped,aciccarello/DefinitelyTyped,scriby/DefinitelyTyped,alexdresko/DefinitelyTyped,martinduparc/DefinitelyTyped,one-pieces/DefinitelyTyped,gcastre/DefinitelyTyped,damianog/DefinitelyTyped,aciccarello/DefinitelyTyped,nycdotnet/DefinitelyTyped,gcastre/DefinitelyTyped,sledorze/DefinitelyTyped,psnider/DefinitelyTyped,rcchen/DefinitelyTyped,schmuli/DefinitelyTyped,hellopao/DefinitelyTyped,benishouga/DefinitelyTyped,AbraaoAlves/DefinitelyTyped,YousefED/DefinitelyTyped,chrootsu/DefinitelyTyped,amanmahajan7/DefinitelyTyped,jimthedev/DefinitelyTyped,johan-gorter/DefinitelyTyped,syuilo/DefinitelyTyped,magny/DefinitelyTyped,jimthedev/DefinitelyTyped,isman-usoh/DefinitelyTyped,borisyankov/DefinitelyTyped,georgemarshall/DefinitelyTyped,mcrawshaw/DefinitelyTyped,johan-gorter/DefinitelyTyped,daptiv/DefinitelyTyped,paulmorphy/DefinitelyTyped,slavomirvojacek/DefinitelyTyped,xStrom/DefinitelyTyped,HPFOD/DefinitelyTyped,jimthedev/DefinitelyTyped,magny/DefinitelyTyped,minodisk/DefinitelyTyped,abbasmhd/DefinitelyTyped,nainslie/DefinitelyTyped,donnut/DefinitelyTyped,isman-usoh/DefinitelyTyped,use-strict/DefinitelyTyped,chrismbarr/DefinitelyTyped,minodisk/DefinitelyTyped,mcrawshaw/DefinitelyTyped,HPFOD/DefinitelyTyped,arusakov/DefinitelyTyped,arma-gast/DefinitelyTyped,arma-gast/DefinitelyTyped,GiedriusGrabauskas/DefinitelyTyped,florentpoujol/DefinitelyTyped,AgentME/DefinitelyTyped,yuit/DefinitelyTyped,florentpoujol/DefinitelyTyped,AgentME/DefinitelyTyped,AbraaoAlves/DefinitelyTyped,pocesar/DefinitelyTyped,gandjustas/DefinitelyTyped,shlomiassaf/DefinitelyTyped,paulmorphy/DefinitelyTyped,chrismbarr/DefinitelyTyped,YousefED/DefinitelyTyped,abner/DefinitelyTyped,newclear/DefinitelyTyped,sledorze/DefinitelyTyped,amir-arad/DefinitelyTyped,progre/DefinitelyTyped,dsebastien/DefinitelyTyped,benishouga/DefinitelyTyped,martinduparc/DefinitelyTyped,zuzusik/DefinitelyTyped,jraymakers/DefinitelyTyped,benishouga/DefinitelyTyped,abbasmhd/DefinitelyTyped,Penryn/DefinitelyTyped