Describe the bug
The RollbarCommon package tests fail to build for iOS.

This is due to two issues:

1. The use of self.className in NSDictionaryRollbarTests.swift which is only available on macOS
2. The use of the .sortedKeys options in JSONSerialization in NSJSONSerializationRollbarTests#testNSJSONSerializationRollbar_safeDataFromJSONObject which is only available on macOs and iOS 11+

To Reproduce
Steps to reproduce the behavior:

1. Open the project
2. Select the RollbarCommon scheme and select an iOS simulator as the target
3. Try to run the tests
4. Tests will not build with errors point at the above description

Expected behavior
The test build and run

Rollbar-Apple SDK version: v...

Calling the SDK from (x-mark all suitable):
[x] Objective-C
[x] Swift
[] Other:

Runtime environment (please complete the following information as applicable):

• OS: [iOS, macOS]
• OS version: Big Sur 11.3