Update .codecov.yml

[CoderZhi]

bump target to 85%

[codecov]

Codecov Report

Merging #3155 (6a8f37c) into master (dd6e430) will decrease coverage by 0.00%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #3155      +/-   ##
==========================================
- Coverage   75.15%   75.14%   -0.01%     
==========================================
  Files         220      220              
  Lines       21001    21001              
==========================================
- Hits        15784    15782       -2     
- Misses       4384     4387       +3     
+ Partials      833      832       -1     

Impacted Files	Coverage Δ
consensus/scheme/rolldpos/rolldposctx.go	73.59% <0.00%> (-0.49%)	⬇️

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