Update pygments minimum dependency version to silence dependabot

[jnwatson]

No description provided.

[codecov]

Codecov Report

Merging #2139 (de891e8) into master (5153287) will decrease coverage by 0.14%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #2139      +/-   ##
==========================================
- Coverage   97.04%   96.90%   -0.15%     
==========================================
  Files         152      152              
  Lines       30703    30703              
==========================================
- Hits        29797    29753      -44     
- Misses        906      950      +44     

Flag	Coverage Δ
linux	96.90% <ø> (-0.15%)	⬇️
linux_replay	?

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Impacted Files	Coverage Δ
synapse/tests/utils.py	93.77% <0.00%> (-2.12%)	⬇️
synapse/lib/hiveauth.py	96.18% <0.00%> (-0.73%)	⬇️
synapse/cortex.py	96.20% <0.00%> (-0.71%)	⬇️
synapse/lib/view.py	94.18% <0.00%> (-0.70%)	⬇️
synapse/lib/link.py	98.32% <0.00%> (-0.56%)	⬇️
synapse/lib/trigger.py	94.11% <0.00%> (-0.43%)	⬇️
synapse/lib/layer.py	98.11% <0.00%> (-0.06%)	⬇️

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