Fix error message formatting (#31338)

Summary:
This error message doesn't format correctly when outputted to the terminal.  It seems the 2nd line is missing

## Changelog

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[iOS] [Fixed] - bug with error message formatting when bundle is missing

Pull Request resolved: #31338

Test Plan:
Before:
![wHHXtKq](https://user-images.githubusercontent.com/4398635/114310176-f11f8700-9ab7-11eb-9de7-b80aab92d440.png)

After:
![6nIjRHc](https://user-images.githubusercontent.com/4398635/114310470-d6014700-9ab8-11eb-9164-d6edde95c6f8.png)

Reviewed By: cipolleschi, sota000

Differential Revision: D30912237

Pulled By: cortinico

fbshipit-source-id: 68a4b29cdd93cbde7ba4611c5e38775561b73ea2

scripts/react-native-xcode.sh

@@ -175,7 +175,6 @@ else
 fi
 
 if [[ $DEV != true && ! -f "$BUNDLE_FILE" ]]; then
-  echo "error: File $BUNDLE_FILE does not exist. This must be a bug with" >&2
-  echo "React Native, please report it here: https://github.com/facebook/react-native/issues"
+  echo "error: File $BUNDLE_FILE does not exist. This must be a bug with React Native, please report it here: https://github.com/facebook/react-native/issues" >&2
   exit 2
 fi