Upgrading solidity-coverage and using new plugin format

[jjgonecrypto]

Fixes coverage reports (thanks to @cgewecke) and adds codecov.io reports via travis

[jjgonecrypto]

@cgewecke do you happen to have any ideas on the above error with the linker?

[cgewecke]

@justinjmoses Will take a look...

[cgewecke]

@justinjmoses #453 has some possible fixes....

[jjgonecrypto]

You're a rockstar @cgewecke 🚀. Do you have an address for donations?

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (develop@87f2f76). Click here to learn what that means.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             develop     #452   +/-   ##
==========================================
  Coverage           ?   87.99%           
==========================================
  Files              ?       47           
  Lines              ?     1941           
  Branches           ?      266           
==========================================
  Hits               ?     1708           
  Misses             ?      233           
  Partials           ?        0

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[cgewecke]

@justinjmoses Oh that's really sweet of you - solidity-coverage 0.7.x was funded by an EF grant and getting it to run on some of the larger, more widely used projects was part of the initial proposal. It's received all the donations it needs, thanks though :)