Fix compatibility issue with wx3

Index: ebook2cwgui.cpp
--- ebook2cwgui.cpp.orig
+++ ebook2cwgui.cpp
@@ -679,8 +679,7 @@ wxString Ebook2cw::FindConfigFile () {
 	/* Otherwise where it "should" be; create if not there */
 
 	wxString dir;
-	wxStandardPaths stdPaths;
-	dir = stdPaths.GetUserConfigDir();
+	dir = wxStandardPaths::Get().GetUserConfigDir();
 
 #ifdef __WXMSW__
 	if (!wxDirExists(dir + wxT("\\ebook2cw"))) {
