Upgrade iOS deployment target to iOS10 from iOS8

[Alex-Navarro-MB]

This pull request includes (pick all that apply):

• Bugfixes
• New features
• Breaking changes
• Documentation updates
• Unit tests
• Other

Summary

Xcode/Platform/Language Compatibility

• Upgrade iOS deployment version from 8 to 12, to resolve errors being generated by fastlane for deployments.

Implementation

• Changed iOS deployment target and related documentation

Test Plan

• Potentially N/A.
  No logic was modified just bumping deployment version.

[eneko]

HI @Alex-Navarro-MB & @brettwellmanmbo, per our recent conversations on our slack channels, we should be able to drop support for anything below iOS 12.

In regards of CI, we would need to migrate this repo to GitHub Actions, since we are not using Travis anymore. Thanks!