v3.1.3 Add concurrent tests in the unit test and Bumps junit from 4.12 to 4.13.1.
- Bumps junit from 4.12 to 4.13.1.
- Add concurrent tests for config in the unit test
- Update wording and grammar readme on Client Initialization and Configuration
- Update Midtrans account for unit test
- Add example of usage method that is safe for concurrent/multi-thread Java implementation