MNT: Fix dc calls

Replace dc calls with syntax that will work on all platforms (dc - is unsupported on new macOS)

extracttxt

@@ -10,15 +10,15 @@ num=`grep -n $1 $2 | head -n 1 | cut -d':' -f1 ` ; export num
 if [ X${num}X != XX ] ; then
   if [ $# -ge 4 ]; then
     if [ $4 -ge 0 ] ; then
-      num1=` echo "$num $4 + p" | dc -` ; export num1
+      num1=` echo "$num $4 + p" | dc` ; export num1
     else
-      num1=` echo "0 0 $4 - $num + p" | dc -` ; export num1
+      num1=` echo "0 0 $4 - $num + p" | dc` ; export num1
     fi
   else
     num1=$num ; export num1
   fi
   if [ $# -ge 3 ]; then
-   num2=` echo "$num1 $3 + 1 - p" | dc -` ; export num2
+   num2=` echo "$num1 $3 + 1 - p" | dc` ; export num2
    if [ $num2 -lt $num1 ]; then
 	num1=$num2 ; export num1
     fi