Directed Graphs

[joleaf]

Hi @TonyZZX ,
thanks a lot for the work!
Are directed graphs supported? :)

Here you fix define the "directed" param as false, I wonder if this algorithm works if this variable is set to true?

gSpan.Java/src/main/java/io/github/tonyzzx/gspan/gSpan.java

Line 65 in 8eac06d

directed = false;