Timestamps have unkeyed field - causes composite literal uses unkeyed fields warning

[envasquez]

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Subject of the issue

• Briefly describe your issue. More details can be added below.

Your environment

• Artifactory version and/or Xray version
  Artifactory version 2.0.0

• Golang version
  go version go1.10.3 darwin/amd64

• Operating System
  Mac OS X: Mojave

• Database type/version (if relevant)
  N/A

Expected behavior

• Tell us what should happen
  No warnings in client code. (in this case, it is in my test code)

Actual behavior

• Tell us what happens instead, including any relevant errors or stack trace
  Compiler warnings

• Verify you have redacted any sensitive hostnames, credentials, application names, etc from these errors/stack traces
  "severity": 4,
  "message": "github.com/target/go-arty/artifactory.Timestamp composite literal uses unkeyed fields",
  "source": "go-vet",
  "startLineNumber": 49,
  "startColumn": 1,
  "endLineNumber": 49,
  "endColumn": 2

Steps to Reproduce

1. See line 43 of timestamp.go
   or this client code will cause the warning as well.
   t := artifactory.Timestamp{time.Now()}