Make Crypto abstract methods public

[jgavris]

It's not currently possible to plug in a custom Crypto implementation for storing analytics events on disk since these abstract methods have default / package visibility.

[codecov-io]

Codecov Report

Merging #632 into master will decrease coverage by 0.27%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #632      +/-   ##
==========================================
- Coverage   83.43%   83.16%   -0.28%     
==========================================
  Files          31       31              
  Lines        2512     2512              
  Branches      292      292              
==========================================
- Hits         2096     2089       -7     
- Misses        329      335       +6     
- Partials       87       88       +1

Impacted Files	Coverage Δ
...cs/src/main/java/com/segment/analytics/Crypto.java	100% <ø> (ø)	⬆️
...java/com/segment/analytics/SegmentIntegration.java	81.9% <100%> (ø)	⬆️
.../src/main/java/com/segment/analytics/ValueMap.java	86.39% <0%> (-2.73%)	⬇️
...ain/java/com/segment/analytics/internal/Utils.java	74.13% <0%> (-1.15%)	⬇️
...cs/src/main/java/com/segment/analytics/Traits.java	92.3% <0%> (-1.1%)	⬇️

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[bsneed]

thanks @jgavris !