Fix "missing argument" error in checking jekyll existence.

PiperOrigin-RevId: 298396725
diff --git a/scripts/serve-docs.sh b/scripts/serve-docs.sh
index 56f0067..24d10e7 100755
--- a/scripts/serve-docs.sh
+++ b/scripts/serve-docs.sh
@@ -72,7 +72,7 @@
 }
 
 check_jekyll() {
-  which $1 > /dev/null || \
+  which jekyll > /dev/null || \
     (
       cat <<EOF
 jekyll not installed. Please install jekyll and rubygem dependencies by going