AOYAMA hiroyuki

Results 2 issues of AOYAMA hiroyuki

- [x] apply Xcode12 recommended settings (`IPHONEOS_DEPLOYMENT_TARGET = 8.0` is no longer supported) - [x] remove VALID_ARCHS because it's deprecated in Xcode12. see [release notes](https://developer.apple.com/documentation/xcode-release-notes/xcode-12-beta-release-notes) for details. I tested with...

I got the following error on linux. ```shell .build/checkouts/JASON/Source/JSONKey.swift:26:8 error: No such module 'CoreGraphics' import CoreGraphics ^ ``` So I remove CoreGraphics dependency for linux.