Combinatorics: fix neighbors(::Graph,::Int64)

changed to take both out- and in-neighbours into account when graph is directed

src/Combinatorics/Graphs/functions.jl

@@ -502,11 +502,18 @@ julia> neighbors(g, 3)
  4
 ```
 """
-function neighbors(g::Graph{T}, v::Int64) where {T <: Union{Directed, Undirected}}
+function neighbors(g::Graph{Undirected}, v::Int64)
     pmg = pm_object(g);
     result = Polymake._outneighbors(pmg, v-1)
     return [x+1 for x in result]
 end
+function neighbors(g::Graph{Directed}, v::Int64)
+    pmg = pm_object(g);
+    result1 = Polymake._outneighbors(pmg, v-1)
+    result2 = Polymake._inneighbors(pmg, v-1)
+    return unique(vcat([x+1 for x in result1],[x+1 for x in result2]))
+end
+
 
 @doc raw"""
     degree(g::Graph{T} [, v::Int64]) where {T <: Union{Directed, Undirected}}