fix(typescript): fix packageJSON type definition

Author: azu

README.md

@@ -40,11 +40,13 @@ Install with [npm](https://www.npmjs.com/):
 ```ts
 export interface rcConfigLoaderOption {
     // does look for `package.json`
-    packageJSON?: boolean,
+    packageJSON?: boolean | {
+        fieldName: string;
+    };
     // if config file name is not same with packageName, set the name
     configFileName?: string;
     // treat default(no ext file) as some extension
-    defaultExtension?: string | string[],
+    defaultExtension?: string | string[];
     // where start to load
     cwd?: string;
 }

src/rc-config-loader.d.ts

@@ -1,6 +1,10 @@
 export interface rcConfigLoaderOption {
     // does look for `package.json`
-    packageJSON?: boolean;
+    packageJSON?:
+        | boolean
+        | {
+              fieldName: string;
+          };
     // if config file name is not same with packageName, set the name
     configFileName?: string;
     // treat default(no ext file) as some extension