Fix typo in installation.md

[Woldelig]

Pull Request Description

Please include a summary of the change request or bug which is supposed to be fixed as part of this pull request

Type of Pull Request

• [ ] New feature/Enhancement - non-breaking change which adds functionality
• [ ] Bug fix
• [ ] Breaking change (Require Major version change?)

Type of Change

• [ ] OpenPeppol AS2/AS4 specification
• [ ] OpenPeppol Spring/Fall release
• [ ] Oxalis software change or enhancement
• [ ] CEF change

Pull Request Checklist:

• [ ] My code follows the style guidelines of this project
• [ ] I have commented my code, particularly in hard-to-understand areas. But did not added unnecessary annotation/comment say @author name etc
• [ ] I have checked my code for variable and method name and corrected grammar/spelling mistakes if any
• [ ] I have made corresponding changes to the documentation where needed
• [ ] My changes generate no new/additional warnings
• [ ] My change is not breaking or creating conflict with associated dependencies
• [ ] I have performed a self-review of my own code
• [ ] I ran mvn clean install before commit and all tests run successfully
• [ ] I conducted basic QA to assure all features are working fine
• [ ] My pull request generate no conflicts with master branch
• [ ] I requested code review from other team members