refactor(bash): avoid messing with syntax highlighting

The backslash character in _osc_end was throwing off syntax highlighting
in vim, so I just use the hex code for \ (0x5c) instead.

roles/bash/files/profile

@@ -239,7 +239,7 @@ _osc_start() {
 # requires ST to end its wrapping DCS.
 _osc_end() {
     if [ -n "$TMUX" ]; then
-        printf "\a\e\\"
+        printf "\a\e\x5c"       # 0x5c == backslash
     else
         printf "\a"
     fi