Add Alexey Shuvaev (shuvaev at physik.uni-wuerzburg.de) to the contributors list.
He is maintainer of x11-toolkits/gtkdatabox, x11-toolkits/slgtk (ports/125055),
devel/slglade (ports/126652) and x11-toolkits/slgtkdatabox (ports/126654).

Approved by: miwi (mentor)