Fix ESM build file names

`tsup` produces two builds - ESM (`.js` files) and CJS (`.cjs`). This commit replaces non-existing paths (`.mjs`)

Fixes #48

Author: ciesiolka

package.json

@@ -22,14 +22,14 @@
         "node": ">=20"
     },
     "main": "./dist/index.cjs",
-    "module": "./dist/index.mjs",
+    "module": "./dist/index.js",
     "types": "./dist/index.d.ts",
     "exports": {
         ".": {
             "types": "./dist/index.d.ts",
-            "import": "./dist/index.mjs",
+            "import": "./dist/index.js",
             "require": "./dist/index.cjs",
-            "default": "./dist/index.mjs"
+            "default": "./dist/index.js"
         }
     },
     "files": [