Cosmwasm 0.6

[ethanfrey]

Closes #13

Updates dependencies to go-cosmwasm 0.6

TODO: update sample escrow contract and uncomment 2 tests

• Targeted PR against correct branch (see CONTRIBUTING.md)

• Linked to github-issue with discussion and accepted design OR link to spec that describes this work.

• Wrote tests

• Updated relevant documentation (docs/)

• Added a relevant changelog entry to the Unreleased section in CHANGELOG.md

• Reviewed Files changed in the github PR explorer

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For Admin Use:

• Added appropriate labels to PR (ex. wip, ready-for-review, docs)
• Reviewers Assigned
• Squashed all commits, uses message "Merge PR #XYZ: [title]" (coding standards)

[codecov-io]

Codecov Report

Merging #25 into master will decrease coverage by 0.4%.
The diff coverage is 43.93%.

@@            Coverage Diff             @@
##           master      #25      +/-   ##
==========================================
- Coverage   61.25%   60.84%   -0.41%     
==========================================
  Files          13       14       +1     
  Lines        1053     1060       +7     
==========================================
  Hits          645      645              
- Misses        349      356       +7     
  Partials       59       59

Impacted Files	Coverage Δ
x/wasm/internal/keeper/querier.go	23.71% <16.66%> (-4.87%)	⬇️
x/wasm/handler.go	83.58% <33.33%> (ø)	⬆️
x/wasm/internal/keeper/keeper.go	65% <60.6%> (+0.1%)	⬆️
x/wasm/internal/keeper/api.go	66.66% <66.66%> (ø)
lcd_test/helpers.go	76.25% <0%> (+0.71%)	⬆️

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