[SCB-351] upgrade Jackson to 2.9.4 to avoid security risk

[yhs0092]

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See details in https://issues.apache.org/jira/browse/SCB-351

[coveralls]

Coverage increased (+0.02%) to 87.148% when pulling 55fec90 on yhs0092:upgrade_Jackson_to_2.9.4 into b0f8224 on apache:master.