[EventLoop] Set travis.yml pecl-libevent version to beta
[EventLoop] Set travis.yml pecl-libevent version to beta

krageon/react,ympons/react,nemurici/react,naroga/react,ericariyanto/react,naroga/react,cystbear/react,cesarmarinhorj/react,ympons/react,reactphp/react,sachintaware/react,cesarmarinhorj/react,ericariyanto/react,FireWalkerX/react,dagopoot/react,FireWalkerX/react,dagopoot/react,cystbear/react,nemurici/react,krageon/react,sachintaware/react