Migrate to `zip32 0.1`

[codecov-commenter]

Codecov Report

Attention: 16 lines in your changes are missing coverage. Please review.

Comparison is base (4b09ef6) 80.91% compared to head (68290a1) 80.64%.

Files	Patch %	Lines
src/zip32.rs	56.00%	11 Missing :warning:
src/keys.rs	28.57%	5 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## zcash_spec-0.1 #414 +/- ## ================================================== - Coverage 80.91% 80.64% -0.27% ================================================== Files 30 30 Lines 3144 3152 +8 ================================================== - Hits 2544 2542 -2 - Misses 600 610 +10 ```

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