dart_sass.bash: fixed shellcheck warning

priv/dart_sass.bash

@@ -19,7 +19,7 @@ exec >/dev/null 2>&1
 # Read from stdin in the background and
 # kill running program when stdin closes
 exec 0<&0 $(
-  while read; do :; done
+  while read -r; do :; done
   kill -KILL $pid1
 ) &
 pid2=$!