Fix tab key

When Shift + Tab is pressed X server send the event XK_ISO_Left_Tab with
ShiftMask, so this is the entry we need in config.def.h

This patch also revert the previous patch for this issue because it breaks
the keyboard.
---
 config.def.h |    2 +-
 st.c         |    2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

st.c

@@ -2700,7 +2700,7 @@ kmap(KeySym k, uint state) {
 		if(kp->k != k)
 			continue;
 
-		if((state & mask) != mask ||
+		if((state & mask) != mask &&
 				(mask == XK_NO_MOD && state)) {
 			continue;
 		}