Consistent chainable mutator behavior (#295)

src/Aggregation/AbstractAggregation.php

src/Aggregation/Bucketing/ChildrenAggregation.php

src/Aggregation/Bucketing/CompositeAggregation.php

src/Aggregation/Bucketing/DateHistogramAggregation.php

src/Aggregation/Bucketing/DateRangeAggregation.php

src/Aggregation/Bucketing/DiversifiedSamplerAggregation.php

src/Aggregation/Bucketing/FilterAggregation.php

src/Aggregation/Bucketing/FiltersAggregation.php

src/Aggregation/Bucketing/GeoDistanceAggregation.php

src/Aggregation/Bucketing/GeoHashGridAggregation.php

src/Aggregation/Bucketing/HistogramAggregation.php

src/Aggregation/Bucketing/NestedAggregation.php

src/Aggregation/Bucketing/RangeAggregation.php

src/Aggregation/Bucketing/ReverseNestedAggregation.php

src/Aggregation/Bucketing/SamplerAggregation.php

src/Aggregation/Matrix/MatrixStatsAggregation.php

src/Aggregation/Metric/CardinalityAggregation.php

src/Aggregation/Metric/ExtendedStatsAggregation.php

src/Aggregation/Metric/GeoBoundsAggregation.php

src/Aggregation/Metric/PercentileRanksAggregation.php