gatsby-browser.js error on gatsby build --prefix-paths

[naqushab]

I forked your blog and tried to build and yarn install and gatsby develop works fine.
But when I use gatsby build or gatsby build --prefix-paths in order to deploy the changes on my gh-pages. It shows this error:

 ~/Documents/blog >$ gatsby build --prefix-paths
success delete html and css files from previous builds — 0.010 s
success open and validate gatsby-config.js — 0.005 s

Your plugins must export known APIs from their gatsby-browser.js.
The following exports aren't APIs. Perhaps you made a typo or
your plugin is outdated?

See https://www.gatsbyjs.org/docs/browser-apis/ for the list of Gatsby Browser APIs
 — Your site's gatsby-browser.js is exporting a variable named "clientEntry" which isn't an API. Perhaps you meant to export "onClientEntry"?

Can you please help me why this is happening? I tried almost everything for this.