Fix warning with is-gen-fn package

[hckhanh]

Every time I install this package, I always see this warning:

(node:10904) [DEP0128] DeprecationWarning: Invalid 'main' field in 'C:\Users\hoang\WebstormProjects\saladin-utils\node_modules\.pnpm\koa-joi-router@8.0.0\node_modules\is-gen-fn\package.json' of 'yes'. Please either fix that or report it to the module author
    at tryPackage (node:internal/modules/cjs/loader:411:15)
    at Module._findPath (node:internal/modules/cjs/loader:613:18)
    at Module._resolveFilename (node:internal/modules/cjs/loader:981:27)
    at Module._load (node:internal/modules/cjs/loader:841:27)
    at Module.require (node:internal/modules/cjs/loader:1061:19)
    at require (node:internal/modules/cjs/helpers:103:18)
    at Object.<anonymous> (C:\Users\hoang\WebstormProjects\saladin-utils\node_modules\.pnpm\koa-joi-router@8.0.0\node_modules\koa-joi-router\joi-router.js:5:17)
    at Module._compile (node:internal/modules/cjs/loader:1159:14)
    at Module._extensions..js (node:internal/modules/cjs/loader:1213:10)
    at Module.load (node:internal/modules/cjs/loader:1037:32)