Adjust comment regarding bug in igraph::disjoint_union

The bug in igraph, which we describe in a comment, affects not only igraph
versions 1.4.0 and 1.4.1, but also affects igraph version 1.4.2, as the bug
was reported after the release of version 1.4.2.
Therefore, adjust our comment accordingly.

This is a follow-up commit for commit a953555.

Signed-off-by: Thomas Bock <bockthom@cs.uni-saarland.de>

util-networks.R

@@ -919,7 +919,7 @@ NetworkBuilder = R6::R6Class("NetworkBuilder",
             ## 1) merge the existing networks
             u = igraph::disjoint_union(authors.net, artifacts.net)
 
-            ## As there is a bug in 'igraph::disjoint_union' in igraph versions 1.4.0 and 1.4.1
+            ## As there is a bug in 'igraph::disjoint_union' in igraph versions 1.4.0, 1.4.1, and 1.4.2
             ## (see https://github.com/igraph/rigraph/issues/761), we need to adjust the type of the date attribute
             ## of the outcome of 'igraph::disjoint_union'.
             ## Note: The following temporary fix only considers the 'date' attribute. However, this problem could also