refactor: solidity version update

[Nipol]

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/HAECHI-LABS/vvisp/blob/master/CONTRIBUTING.md#commit
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)
• PR to dev branch

PR Type

What kind of change does this PR introduce?

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Documentation content changes
• Other... Please describe: changed the version of Smart contract and solc to 0.5.

What is the current behavior?

Issue Number: N/A

What is the new behavior?

Use the solc 0.5

Does this PR introduce a breaking change?

• Yes
• No

Other information

[coveralls]

Pull Request Test Coverage Report for Build 403

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+23.9%) to 86.765%

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Totals
Change from base Build 397:	23.9%
Covered Lines:	722
Relevant Lines:	823

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💛 - Coveralls

[JhChoy]

This will conflict with #97; merge this later.