Fix link in README.md

[carschno]

See #5

[carschno]

For some reason, the link checks pass fine when I run them locally (except for the relative link, can be ignored):

% ./markdown-link-check https://raw.githubusercontent.com/nlesc-sigs/nlp-sig/master/README.md

FILE: https://raw.githubusercontent.com/nlesc-sigs/nlp-sig/master/README.md
  [✖] #upcoming-meetings
  [✓] https://www.esciencecenter.nl/team/carsten-schnober/
  [✓] https://www.esciencecenter.nl/team/dr-laura-ootes/
  [✓] https://www.esciencecenter.nl/team/dr-ir-erik-tjong-kim-sang/
  [✓] https://www.esciencecenter.nl/fellowship-programme/claudiu-forgaci/
  [✓] https://github.com/UD3-Lab/mintEMU
  [✓] https://github.com/nlesc-sigs/nlp-sig/blob/master/meetings.md
  [✓] nlp-conferences.md
  [✓] nlp-literature.md
  [✓] https://www.aclweb.org/portal/
  [✓] https://www.let.rug.nl/vannoord/Clin/
  [✓] https://www.clinjournal.org/clinj
  [✓] https://notas.nl/
  [✓] https://www.let.rug.nl/vannoord/TST-Geschiedenis/

  14 links checked.

  ERROR: 1 dead links found!
  [✖] #upcoming-meetings → Status: 404