Update ShowExceptions to suit latest rack master
Update ShowExceptions to suit latest rack master

* Post 893a2c50 in rack/rack, the #pretty method used while generating
  the HTML error markup, implemented in Rack::ShowExceptions, returns a
  String instead of an Array. This change uses Array() to
  convert the exception string in both plain text and HTML modes
  to an array.

kyontan/sinatra,miyazawatomoka/sinatra,ktw1222/sinatra,dariubs/sinatra,porras/sinatra,DoraALin/sinatra,nicoayala/sinatra,gferguson-gd/sinatra,defsprite/sinatra,mwpastore/sinatra,eileencodes/sinatra,mwpastore/sinatra,Rayheng/sinatra,JonMidhir/sinatra,ktw1222/sinatra,guidohcosta/sinatra,emiliocorpus/sinatra,ksw2599/sinatra,DoraALin/sinatra,ABaldwinHunter/sinatra-classic,porras/sinatra,jkowens/sinatra,ganmacs/sinatra,d-bot/sinatra,ABaldwinHunter/sinatra-classic,ganmacs/sinatra,ksw2599/sinatra,nicoayala/sinatra,siberianbear/sinatra,dariubs/sinatra,JonRowe/sinatra,midorineko/sinatra,JonMidhir/sinatra,burningTyger/sinatra,davydovanton/sinatra,Wirachmat/sinatra,gferguson-gd/sinatra,JonMidhir/sinatra,wzheng1/sinatra,kumji/sinatra,miyazawatomoka/sinatra,frechei/sinatra,burningTyger/sinatra,mwpastore/sinatra,jenalgit/sinatra,ryanshaw/sinatra,emiliocorpus/sinatra,davydovanton/sinatra,sinatra/sinatra,ryanshaw/sinatra,RosenDimov/sinatra,autopp/sinatra,lastcat/sinatra,defsprite/sinatra,laplaceliu/sinatra,cyberid41/sinatra,trexnix/sinatra,trexnix/sinatra,sethuster/sinatra,guidohcosta/sinatra,burningTyger/sinatra,howtolearntocode/sinatra,nju520/sinatra,kumji/sinatra,d-bot/sinatra,kyontan/sinatra,eileencodes/sinatra,JonRowe/sinatra,lastcat/sinatra,sethuster/sinatra,sinatra/sinatra,wzheng1/sinatra,RosenDimov/sinatra,jenalgit/sinatra,QLGu/sinatra,midorineko/sinatra,Wirachmat/sinatra,siberianbear/sinatra,jkowens/sinatra,howtolearntocode/sinatra,Rayheng/sinatra,jkowens/sinatra,laplaceliu/sinatra,frechei/sinatra,nju520/sinatra,autopp/sinatra,cyberid41/sinatra,QLGu/sinatra