remove typo extra underscore

Author: peilingjiang

src/content/configuration/output.mdx

@@ -924,7 +924,7 @@ Configure how the library will be exposed.
 
   Types included by default are `'var'`, `'module'`, `'assign'`, `'assign-properties'`, `'this'`, `'window'`, `'self'`, `'global'`, `'commonjs'`, `'commonjs2'`, `'commonjs-module'`, `'commonjs-static'`, `'amd'`, `'amd-require'`, `'umd'`, `'umd2'`, `'jsonp'` and `'system'`, but others might be added by plugins.
 
-For the following examples, we'll use `__entry_return_` to indicate the values returned by the entry point.
+For the following examples, we'll use `_entry_return_` to indicate the values returned by the entry point.
 
 #### Expose a Variable