pcat: fix copy&paste error defining GREP

Signed-off-by: Alejandro Mery <amery@geeks.cl>

files/bin/pcat

@@ -21,7 +21,7 @@ if [ -n "$(sed 2>&1 | grep -- -u,)" ]; then
 else
 	SED="${STDBUF:+$STDBUF }sed"
 fi
-GREP="${STDBUF:+$STDBUF }sed"
+GREP="${STDBUF:+$STDBUF }grep"
 
 # Colours
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