We need to prove that $$\sum_{cyc}(a-b)(a-c)(a-d)(a-e)\geq0.$$ Let $a\geq b\geq c\geq d\geq e$.
Thus, $$(c-a)(c-b)(c-d)(c-e)\geq0,$$ $$(a-b)(a-c)(a-d)(a-e)+(b-a)(b-c)(b-d)(b-e)=$$ $$=(a-b)((a-c)(a-d)(a-e)-(b-e)(b-c)(b-d))\geq0$$ and $$(d-a)(d-b)(d-c)(d-e)+(e-a)(e-b)(e-c)(e-d)=$$ $$=(d-e)((a-e)(b-e)(c-e)-(a-d)(b-d)(c-d))\geq0$$ and we are done!