minor #9827 Update typescript.rst (kallard1)

This PR was submitted for the 4.0 branch but it was merged into the 3.4 branch instead (closes #9827).

Discussion
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Update typescript.rst

`configFileName` was renamed in `configFile` for Typescript configuration

```
Module build failed: Error: ts-loader was supplied with an unexpected loader option: configFileName

Please take a look at the options you are supplying; the following are valid options:
silent / logLevel / logInfoToStdOut / instance / compiler / context / configFile / transpileOnly / ignoreDiagnostics / errorFormatter / colors / compilerOptions / appendTsSuffixTo / appendTsxSuffixTo / onlyCompileBundledFiles / happyPackMode / getCustomTransformers / reportFiles / experimentalWatchApi / allowTsInNodeModules
```

Commits
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e2cf45c Update typescript.rst

Author: javiereguiluz

frontend/encore/typescript.rst

@@ -28,7 +28,7 @@ also configure the `ts-loader options`_ via a callback:
 
     .enableTypeScriptLoader(function (typeScriptConfigOptions) {
         typeScriptConfigOptions.transpileOnly = true;
-        typeScriptConfigOptions.configFileName = '/path/to/tsconfig.json';
+        typeScriptConfigOptions.configFile = '/path/to/tsconfig.json';
     });
 
 If React assets are enabled (``.enableReactPreset()``), any ``.tsx`` file will be