Fix shellcheck issue SC2217 in run_calltool.sh

scripts/maint/run_calltool.sh

@@ -18,7 +18,7 @@ for calculation in $SUBITEMS; do
   python -m calltool "$calculation" > callgraph/"$calculation"
 done
 
-echo <<EOF > callgraph/README
+cat <<EOF > callgraph/README
 This directory holds output from calltool, as run on Tor.  For more
 information about each of these files, see the NOTES and README files in
 the calltool distribution.