Fix typo in comment of hack/verify-shellcheck.sh

Signed-off-by: Ma Xinjian <[email protected]>

Author: Ma Xinjian

hack/verify-shellcheck.sh

@@ -136,7 +136,7 @@ fi
 # common arguments we'll pass to shellcheck
 SHELLCHECK_OPTIONS=(
   # allow following sourced files that are not specified in the command,
-  # we need this because we specify one file at at time in order to trivially
+  # we need this because we specify one file at a time in order to trivially
   # detect which files are failing
   "--external-sources"
   # include our disabled lints