Update scio to 0.13.6

[RustedBones]

This is not ideal, but force the avro coder to use the reflect API so CharSequence implementation is String.
When it is Utf8, AvroDiffy implementation emits Delta of distance zero

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (46adba7) 71.24% compared to head (6a8f241) 71.24%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #689   +/-   ##
=======================================
  Coverage   71.24%   71.24%           
=======================================
  Files          40       40           
  Lines        1749     1749           
  Branches      254      254           
=======================================
  Hits         1246     1246           
  Misses        503      503           

Flag	Coverage Δ
ratatoolCli	2.99% <ø> (ø)
ratatoolCommon	∅ <ø> (∅)
ratatoolDiffy	31.42% <100.00%> (ø)
ratatoolExamples	15.91% <100.00%> (ø)
ratatoolSampling	62.26% <100.00%> (ø)
ratatoolScalacheck	81.71% <100.00%> (ø)
ratatoolShapeless	4.31% <ø> (ø)

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