fix shellcheck errors for 2020/burton/check_be.sh

2020/burton/check_be.sh

@@ -1,12 +1,12 @@
 #!/usr/bin/env bash
 
 prog="$1"
-: ${prog:=./prog_be}
+: "${prog:=./prog_be}"
 
 check_code() {
-    /bin/echo -n "$1 "; $prog $1 | rev
+    /bin/echo -n "$1 "; $prog "$1" | rev
 }
 
-seq 0 255 | while read a; do
+seq 0 255 | while read -r a; do
     check_code "$a"
 done | pr -t -w120 -8