change .solcoverjs occurencies to .solcover.js

[joaoh9]

small change than could save people some time :)

[codecov-commenter]

Codecov Report

Base: 95.90% // Head: 95.90% // No change to project coverage 👍

Coverage data is based on head (7dfb107) compared to base (8d49be0).
Patch has no changes to coverable lines.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #777   +/-   ##
=======================================
  Coverage   95.90%   95.90%           
=======================================
  Files          19       19           
  Lines        1050     1050           
=======================================
  Hits         1007     1007           
  Misses         43       43           

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[cgewecke]

Thanks! (Sorry for the delay merging this)