bump dogstatsd-ruby to 4.5.0
bump dogstatsd-ruby to 4.5.0

https://github.com/DataDog/dogstatsd-ruby/blob/master/CHANGELOG.md

Change-Id: Ide95da19341d93c2fd9a470da8e696c3619146fa
Reviewed-on: https://gerrit.instructure.com/212339
Tested-by: Jenkins
Reviewed-by: James Butters <4c5a489c9bb72d41f20b3b22aaf4c9b864e32f20@instructure.com>
QA-Review: Simon Williams <088e16a1019277b15d58faf0541e11910eb756f6@instructure.com>
Product-Review: Simon Williams <088e16a1019277b15d58faf0541e11910eb756f6@instructure.com>

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