Use object assign for node6

[arjd4science]

• improves coverage by removing unused functions and condensing lines
• uses Object.assign instead of ... rest operator to support node6

[coveralls]

Coverage increased (+5.0%) to 82.963% when pulling abe83f3 on arjd4science:use-object-assign-for-node6 into 4eafeb1 on vanthome:master.

[vanthome]

Goal is not to support node6 with this module but I will accept it. Also I'm not so happy that you removed the query methods but when needed I can restore them. I want to use them when winston 3 supports querying again.