OPENNLP-1472 Fix flaky (sub-) test of GradientDescentUtilsTest in sandbox component 'nlp-utils' (#88)

- adjusts parameter alpha in GradientDescentUtilsTest from `0.00002` to `0.00001`
- aforementioned param change results in stable convergence, checked via RepeatedTest (JUnit)
- optimizes how random values are obtained in `GradientDescentUtils`
- fixes a potentially unpredictable BigDecimal value in `AnomalyDetectionUtils` (see JavaDoc of that constructor)
3 files changed