'make serve' fails
The target 'serve' in the Makefile fails locally with:
jekyll serve
Configuration file: /home/sluedtke/swc/2019-11-26-potsdam-berlin-R/_config.yml
Source: /home/sluedtke/swc/2019-11-26-potsdam-berlin-R
Destination: /home/sluedtke/swc/2019-11-26-potsdam-berlin-R/_site
Incremental build: disabled. Enable with --incremental
Generating...
Liquid Exception: Liquid syntax error (line 20): Unknown tag 'link' in _includes/navbar.html, included in _layouts/base.html
jekyll 3.1.6 | Error: Liquid syntax error (line 20): Unknown tag 'link'
Makefile:26: recipe for target 'serve' failed
any ideas