crypto/hd: add 'm/' prefix to hd path

[fedekunze]

The original issue was filed against Ethermint:
cosmos/ethermint#605
Thanks: @xiangjianmeng for the original bug report.

From: #7970
Closes: #7966

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Before we can merge this PR, please make sure that all the following items have been
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write a little note why.

• 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
• Review Codecov Report in the comment section below once CI passes

[codecov]

Codecov Report

Merging #7977 (cbb8ff4) into launchpad/backports (7b152b3) will increase coverage by 0.01%.
The diff coverage is 96.00%.

@@                   Coverage Diff                   @@
##           launchpad/backports    #7977      +/-   ##
=======================================================
+ Coverage                50.28%   50.29%   +0.01%     
=======================================================
  Files                      338      338              
  Lines                    17560    17570      +10     
=======================================================
+ Hits                      8830     8837       +7     
- Misses                    7937     7940       +3     
  Partials                   793      793              

[lgtm-com]

This pull request fixes 1 alert when merging 186a352 into 7b152b3 - view on LGTM.com

fixed alerts:

• 1 for Incorrect conversion between integer types

[lgtm-com]

This pull request fixes 1 alert when merging 323988f into 36ff5ca - view on LGTM.com

fixed alerts:

• 1 for Incorrect conversion between integer types

[alessio]

@fedekunze this was a testable example, you turned it into a standard test case (ExampleSomeBIP32TestVecs() -> TestBIP32Vecs(t *testing.T)). Mind elaborating why?

[fedekunze]

what's the purpose of a testable example?

[lgtm-com]

This pull request fixes 1 alert when merging 52b9730 into 69f6ec2 - view on LGTM.com

fixed alerts:

• 1 for Incorrect conversion between integer types

[odeke-em]

Ensures that we catch regressions in functional code the way the callers of the APIs will experience it, also aids in ease documentation without code going out of date when code changes.

…

On Thu, Nov 19, 2020 at 4:28 AM Federico Kunze ***@***.***> wrote: ***@***.**** commented on this pull request. ------------------------------ In crypto/keys/hd/hdpath_test.go <#7977 (comment)>: > - // INVALID - // INVALID // what's the purpose of a testable example? — You are receiving this because your review was requested. Reply to this email directly, view it on GitHub <#7977 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/ABFL3V3ZPIMPT2TKCFXS5X3SQUFOBANCNFSM4T2L7TEQ> .

[lgtm-com]

This pull request fixes 1 alert when merging 65fcb82 into 69f6ec2 - view on LGTM.com

fixed alerts:

• 1 for Incorrect conversion between integer types

[lgtm-com]

This pull request fixes 1 alert when merging cbb8ff4 into 69f6ec2 - view on LGTM.com

fixed alerts:

• 1 for Incorrect conversion between integer types

[alessio]

@ethanfrey @clevinson your approval is required here

[ethanfrey]

Ack