fix shellcheck errors in 2020/burton/check_le.sh

2020/burton/check_le.sh

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