message: Fix: `purser-core` bn validators test
  bn.js does no longer validate the '10e18' string, which one of
  the unit tests was using as an validation example.
  From now on large integers will need to use the long form notation
diff: @@ -14,7 +14,6 @@ describe('`Core` Module', () => {
  test("But passes if it's a valid bigNumber", () => {
  expect(bigNumberValidator(bigNumber(0))).toBeTruthy();
  expect(bigNumberValidator(bigNumber('0'))).toBeTruthy();
  - expect(bigNumberValidator(bigNumber('1e18'))).toBeTruthy();
  expect(bigNumberValidator(bigNumber('9007199254740992'))).toBeTruthy();
  });
  });
  