add python27 support by using reduce instead of max
add python27 support by using reduce instead of max

nicoddemus/pytest,The-Compiler/pytest,pytest-dev/pytest,RonnyPfannschmidt/pytest,pfctdayelise/pytest,alfredodeza/pytest,tomviner/pytest,ddboline/pytest,tomviner/pytest,Akasurde/pytest,hackebrot/pytest,nicoddemus/pytest,markshao/pytest,The-Compiler/pytest,txomon/pytest