Fix for incorrect calculation of betweenness in addNodeSize()

[aj2duncan]

What my pull fixes (if applicable)

When tmp_graph is created in addNodeSize(), the default it to create a directed graph, this will change the values of some of the calculated metrics.

What my pull improves (if applicable)

Adding directed = FALSE so the previous and I think expected behaviour returns.

Confirmation that you have tested your code

library(sigmaNet)
library(igraph)
#create a graph
sig = sigmaFromIgraph(lesMis)

# what the default values should be
betweenness(lesMis)
# values currently used by addNodeSize()
betweenness(graph_from_data_frame(sig$x$graph$edges))
# putting directed = FALSE in gets back to what I think the expected result should be
betweenness(graph_from_data_frame(sig$x$graph$edges, directed = FALSE))

I don't know if you're planning on dealing with directed networks (or give users the option to) but I hope this helps.