VirtualMachineError fixes

[iamdefinitelyahuman]

What I did

• Improve handling of VirtualMachineError in brownie.reverts
• Raise ValueError when the returned RPC error does not contain a data field.

How to verify it

Run tests.

[codecov-commenter]

Codecov Report

Merging #555 into master will decrease coverage by 0.08%.
The diff coverage is 60.00%.

@@            Coverage Diff             @@
##           master     #555      +/-   ##
==========================================
- Coverage   88.12%   88.03%   -0.09%     
==========================================
  Files          56       56              
  Lines        6309     6312       +3     
  Branches     1395     1396       +1     
==========================================
- Hits         5560     5557       -3     
- Misses        517      520       +3     
- Partials      232      235       +3     

Impacted Files	Coverage Δ
brownie/test/managers/runner.py	85.57% <33.33%> (-0.84%)	⬇️
brownie/exceptions.py	84.31% <100.00%> (+0.15%)	⬆️
brownie/network/account.py	91.18% <0.00%> (-1.77%)	⬇️

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