fix: handle missing HEAD^ in vercel ignore script

Author: ArnavJoshi6391

vercel-ignore.sh

@@ -1,3 +1,8 @@
+# Handle initial commits and shallow clones
+if ! git rev-parse --verify HEAD^ >/dev/null 2>&1; then
+  exit 1
+fi
+
 CHANGED_FILES=$(git diff --name-only HEAD^ HEAD)
 
 if [ -z "$CHANGED_FILES" ]; then