Remove ending slash from NGINX_BASE_URL definition

[AlexGacon]

Description

With an external domain, the geoserver oauth is not working correctly: an error message complains about the redirect_uri which does not match what is registered in geonode, because of an additional /.

Type of Change

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• [x] Bug fix
• [ ] New feature
• [ ] Documentation update
• [ ] Refactoring
• [ ] Other (please describe)

Related Issue

If there is an existing issue related to this pull request, please reference it here.

closes #136

Checklist

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• The pull request is limited to one type (docs, feature, bug fix, etc.)
• The pull request is as small as possible. Consider opening multiple pull requests instead of one large one.
• The feature or bug fix has been discussed and documented in an issue beforehand.

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[AlexGacon]

If ok, I can take care of preparing the documentation for a new release.

[AlexGacon]

@mwallschlaeger is it possible to have a review?