sites -> apps copy change

Co-authored-by: ehmicky <ehmicky@users.noreply.github.com>

Author: lindsaylevine

index.js

@@ -44,7 +44,7 @@ module.exports = {
     const isAlreadyUsingNextOnNetlify = hasNextOnNetlifyInstalled || hasNextOnNetlifyPostbuildScript
     if (isAlreadyUsingNextOnNetlify) {
       return failBuild(
-        `This plugin does not support apps that manually use next-on-netlify. Uninstall next-on-netlify as a dependency to resolve.`,
+        `This plugin does not support sites that manually use next-on-netlify. Uninstall next-on-netlify as a dependency to resolve.`,
       )
     }