Bank Account: race detector not run

[bitfield]

Solution 88c019dd66f14fd088b1fbc26af734e8 does not obtain the mutex when calling Balance, yet the tests pass. For this exercise, the tests need to be run with the -race flag to catch data races.

[junedev]

Thanks for the hint! The test runner currently does not include this capability. I created an issue for this in the test runner repo: exercism/go-test-runner#62 Once that issue is addressed, we can use the capability for the bank account exercise.