fix: findup until root from user cwd

Author: pi0

src/_utils.ts

@@ -13,7 +13,7 @@ export async function findup<T>(
   const segments = normalize(cwd).split("/");
 
   while (segments.length > 0) {
-    const path = segments.join("/");
+    const path = segments.join("/") || "/";
     const result = await match(path);
 
     if (result || !options.includeParentDirs) {

src/package-manager.ts

@@ -76,7 +76,7 @@ export async function detectPackageManager(
   options: DetectPackageManagerOptions = {},
 ): Promise<PackageManager | undefined> {
   const detected = await findup(
-    cwd,
+    resolve(cwd || "."),
     async (path) => {
       // 1. Use `packageManager` field from package.json
       if (!options.ignorePackageJSON) {