Fix tab key

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(-)