Fix typo in signed-off-by check error message

Signed-off-by: Fabio Utzig <utzig@apache.org>
diff --git a/scripts/check-signed-off-by.sh b/scripts/check-signed-off-by.sh
index 3346347..45adec7 100755
--- a/scripts/check-signed-off-by.sh
+++ b/scripts/check-signed-off-by.sh
@@ -50,7 +50,7 @@
     echo -e "Missing \"${author}\" in commit ${sha}"
   fi
   if [[ ${found_committer} == false ]]; then
-    echo -e "Missing \"${commiter}\" in commit ${sha}"
+    echo -e "Missing \"${committer}\" in commit ${sha}"
   fi
   if [[ ${found_author} == false || ${found_committer} == false ]]; then
     exit 1