Replace deprecated `index` function
Replace deprecated `index` function

http://pubs.opengroup.org/onlinepubs/009695399/functions/index.html

0re5ama/bspwm,baskerville/bspwm,Stebalien/bspwm,jbalint/bspwm,Stebalien/bspwm,nfnty/bspwm,medisun/bspwm,nfnty/bspwm,baskerville/bspwm,JBouron/bspwm,XiKuuKy/bspwm,nfnty/bspwm,jbalint/bspwm,JBouron/bspwm,medisun/bspwm,0re5ama/bspwm,XiKuuKy/bspwm,ikn/bspwm,ikn/bspwm,netzverweigerer/bspwm,medisun/bspwm,0re5ama/bspwm,netzverweigerer/bspwm,jbalint/bspwm,JBouron/bspwm