Update docs/config/extensions/custom.mdx

Co-authored-by: coderabbitai[bot] <136622811+coderabbitai[bot]@users.noreply.github.com>

Author: ericallam

docs/config/extensions/custom.mdx

@@ -4,7 +4,7 @@ sidebarTitle: "Custom"
 description: "Customize how your project is built and deployed to Trigger.dev with your own custom build extensions"
 ---
 
-Build extension allow you to hook into the build system and customize the build process or the resulting bundle and container image (in the case of deploying). See our [build extension overview](/config/extensions/overview) for more information on how to install and use our built-in extensions. Build extensions can do the following:
+Build extensions allow you to hook into the build system and customize the build process or the resulting bundle and container image (in the case of deploying). See our [build extension overview](/config/extensions/overview) for more information on how to install and use our built-in extensions. Build extensions can do the following:
 
 - Add additional files to the build
 - Add dependencies to the list of externals