Removed mod=readonly from local build and upgraded to go 1.13

[shanev]

• [ ] Linked to Github issues that this PR fixes (if any)
• [ ] Wrote tests
• [ ] Updated README.md if needed
• [ ] Updated docs/spec if needed
• [x] Tested running truchain, truapi, and truapp locally (https://gist.github.com/shanev/3897a80072ac4147677fa596ada497fb)
• [x] Tested exporting state

Upgraded go to 1.13 to make the next upgrade easier. So don't have to switch go versions when setting up testnet.

-mod=readonly was causing old versions of Tendermint to stick around.

[codecov[bot]]

Codecov Report

Merging #810 into develop will not change coverage. The diff coverage is n/a.

@@           Coverage Diff            @@
##           develop     #810   +/-   ##
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  Coverage    58.68%   58.68%           
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  Files           73       73           
  Lines         4175     4175           
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  Hits          2450     2450           
  Misses        1515     1515           
  Partials       210      210