Using part of speech "tag" in system test. (#3471)
Using part of speech "tag" in system test. (#3471)

Token.part_of_speech is now a PartOfSpeech rather than a string
scalar. (This test breakage was accidentally introduced in
googleapis/google-cloud-python,GoogleCloudPlatform/gcloud-python,jonparrott/gcloud-python,calpeyser/google-cloud-python,tswast/google-cloud-python,jonparrott/google-cloud-python,tseaver/gcloud-python,calpeyser/google-cloud-python,GoogleCloudPlatform/gcloud-python,tseaver/google-cloud-python,tseaver/gcloud-python,googleapis/google-cloud-python,tseaver/google-cloud-python,tartavull/google-cloud-python,dhermes/google-cloud-python,jonparrott/gcloud-python,jonparrott/google-cloud-python,dhermes/gcloud-python,tswast/google-cloud-python,tseaver/google-cloud-python,dhermes/google-cloud-python,tartavull/google-cloud-python,dhermes/gcloud-python,tswast/google-cloud-python,dhermes/google-cloud-python