[cosmiconfig] correct filePath to filepath

It should be `filepath` as can be seen in the code:
https://github.com/davidtheclark/cosmiconfig/blob/3e68a30161fcb65296eed26a31cd7dc42bcbb791/src/createExplorer.js#L237

Also in the document: https://github.com/davidtheclark/cosmiconfig#result

types/cosmiconfig/index.d.ts

@@ -14,7 +14,7 @@ export interface Config {
 
 export type CosmiconfigResult = {
   config: Config;
-  filePath: string;
+  filepath: string;
   isEmpty?: boolean;
 } | null;