Fix build-lib script for BSD sed
Fix build-lib script for BSD sed

Summary: GNU and BSD `sed` have some differences. Make the script compatible with both by
using neither of them.
Closes https://github.com/facebook/relay/pull/432

Reviewed By: @josephsavona

Differential Revision: D2514495

fb-gh-sync-id: da914f2c60149a1817e4a6cab6edc6465521d231

cesarandreu/relay,wincent/relay,voideanvalue/relay,Aweary/relay,venepe/relay,mroch/relay,NevilleS/relay,cpojer/relay,voideanvalue/relay,yungsters/relay,chirag04/relay,cpojer/relay,Aweary/relay,cpojer/relay,IlyasM/relayWorking,chirag04/relay,venepe/relay,IlyasM/relayWorking,cesarandreu/relay,zpao/relay,xuorig/relay,dbslone/relay,heracek/relay,chentsulin/relay,voideanvalue/relay,kassens/relay,atxwebs/relay,xuorig/relay,iamchenxin/relay,voideanvalue/relay,mroch/relay,facebook/relay,andimarek/generic-relay,benjaminogles/relay,wincent/relay,xuorig/relay,chentsulin/relay,wincent/relay,facebook/relay,chentsulin/relay,rosskevin/relay,benjaminogles/relay,josephsavona/relay,Aweary/relay,heracek/relay,xuorig/relay,venepe/relay,forter/generic-relay,andimarek/generic-relay,NevilleS/relay,almasakchabayev/relay,apalm/relay,yungsters/relay,almasakchabayev/relay,Shopify/relay,josephsavona/relay,facebook/relay,voideanvalue/relay,zpao/relay,freiksenet/relay,kassens/relay,iamchenxin/relay,zpao/relay,benjaminogles/relay,josephsavona/relay,gabelevi/relay,wincent/relay,voideanvalue/relay,atxwebs/relay,cpojer/relay,iamchenxin/relay,Shopify/relay,freiksenet/relay,NevilleS/relay,rosskevin/relay,gabelevi/relay,cesarandreu/relay,michaelchum/relay,chirag04/relay,dbslone/relay,facebook/relay,heracek/relay,michaelchum/relay,mroch/relay,wincent/relay,xuorig/relay,kassens/relay,atxwebs/relay,wincent/relay,xuorig/relay,michaelchum/relay,andimarek/generic-relay,facebook/relay,apalm/relay,gabelevi/relay,atxwebs/relay,freiksenet/relay,iamchenxin/relay,kassens/relay,yungsters/relay,apalm/relay,kassens/relay,almasakchabayev/relay,Shopify/relay,kassens/relay,facebook/relay,IlyasM/relayWorking