Fix Issue 429

[desperadomzc]

Modify the method printUage() in file: src/main/java/org/jabref/cli/JabRefCLI.java

Make the import and export format of cli output consistent.

Fixes JabRef#429

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1. Change in CHANGELOG.md described in a way that is understandable for the average user (if applicable)
2. Tests created for changes (if applicable)
3. Manually tested changed features in running JabRef (always required)
4. Screenshots added in PR description (for UI changes)
5. Checked developer's documentation: Is the information available and up to date? If not, I outlined it in this pull request.
6. Checked documentation: Is the information available and up to date? If not, I created an issue at https://github.com/JabRef/user-documentation/issues or, even better, I submitted a pull request to the documentation repository.