Add a newline at the end of generated composer.json

It is frustrating that every time I edit `composer.json` with a text editor, I get "generated files are out of sync" errors due to `generator` _not_ putting a newline there

(FWIW, POSIX says that text files should always end with a newline character too)

Author: shish

composer.json

@@ -108,4 +108,4 @@
         "cs-fix": "phpcbf",
         "cs-check": "phpcs"
     }
-}
+}

generator/src/Generator/ComposerJsonEditor.php

@@ -23,7 +23,7 @@ public static function editComposerFileForGeneration(array $modules): void
         $composerJson = \json_decode($composerContent, true);
         $composerJson['autoload']['files'] = self::editFilesListForGeneration($composerJson['autoload']['files'], $modules);
 
-        $newContent = \json_encode($composerJson, \JSON_PRETTY_PRINT | \JSON_UNESCAPED_SLASHES);
+        $newContent = \json_encode($composerJson, \JSON_PRETTY_PRINT | \JSON_UNESCAPED_SLASHES) . "\n";
         \file_put_contents(FileCreator::getSafeRootDir() . '/composer.json', $newContent);
     }