Bump circleci cache for linux ci builds

[vEpiphyte]

Cached builds using multidict 4.7.0 fail. 4.7.1 is working for us now.

related:
aio-libs/multidict#418

[codecov]

Codecov Report

Merging #1462 into master will decrease coverage by 0.03%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1462      +/-   ##
==========================================
- Coverage   95.39%   95.35%   -0.04%     
==========================================
  Files         133      133              
  Lines       20472    20472              
==========================================
- Hits        19529    19522       -7     
- Misses        943      950       +7

Flag	Coverage Δ
#linux	95.35% <ø> (ø)	⬆️
#osx	?

Impacted Files	Coverage Δ
synapse/lib/platforms/darwin.py	0% <0%> (-100%)	⬇️
synapse/lib/thisplat.py	58.33% <0%> (-8.34%)	⬇️
synapse/lib/link.py	98.54% <0%> (-0.73%)	⬇️
synapse/lib/lmdbslab.py	98.91% <0%> (-0.16%)	⬇️

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