config: add Shift+Insert as selpaste() again

This was changed before in:
commit 20f713548de451b67db3306cf8cf7b2f38fee05c on Wed Jan 25 19:17:38 2017

config.def.h

@@ -176,6 +176,7 @@ static Shortcut shortcuts[] = {
 	{ TERMMOD,              XK_C,           clipcopy,       {.i =  0} },
 	{ TERMMOD,              XK_V,           clippaste,      {.i =  0} },
 	{ TERMMOD,              XK_Y,           selpaste,       {.i =  0} },
+	{ ShiftMask,            XK_Insert,      selpaste,       {.i =  0} },
 	{ TERMMOD,              XK_Num_Lock,    numlock,        {.i =  0} },
 };