APP: change app binary name from `certik` to `shentud`

[yoongbok-lee]

Closes: #XXX Related: #XXX

Description

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For contributor use:

• [ ] 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.
• [ ] Code follows the module structure standards.
• [ ] Wrote unit and integration tests
• [ ] Updated relevant documentation (docs/) or specification (x/<module>/spec/)
• [ ] Added relevant godoc comments.
• [ ] Added a relevant changelog entry to the Unreleased section in CHANGELOG.md
• [ ] Re-reviewed Files changed in the Github PR explorer

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For admin use:

• [ ] Added appropriate labels to PR (ex. WIP, R4R, docs, etc)
• [ ] Reviewers assigned
• [ ] Squashed all commits, uses message "Merge pull request #XYZ: [title]"

[codecov[bot]]

Codecov Report

Merging #467 (4b91246) into master (84354a9) will not change coverage. The diff coverage is n/a.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #467   +/-   ##
=======================================
  Coverage   41.30%   41.30%           
=======================================
  Files         123      123           
  Lines       11270    11270           
=======================================
  Hits         4655     4655           
  Misses       6161     6161           
  Partials      454      454           

Impacted Files	Coverage Δ
app/app.go	86.54% <ø> (ø)
app/config.go	0.00% <ø> (ø)
app/encoding.go	100.00% <ø> (ø)
app/export.go	42.50% <ø> (ø)
app/forks.go	0.00% <ø> (ø)
app/mva/forks.go	53.52% <ø> (ø)
x/cvm/keeper/msg_server.go	3.44% <0.00%> (ø)

[yoongbok-lee]

Is it necessary to generate new docs/shentu files?

yes I think so. I'll include them