BigQuery: fix typo in Client docstrings (#5342)
BigQuery: fix typo in Client docstrings (#5342)

Was missing a comma between types in get_job and cancel_job functions.
googleapis/google-cloud-python,googleapis/google-cloud-python,tswast/google-cloud-python,dhermes/gcloud-python,tseaver/gcloud-python,dhermes/google-cloud-python,tswast/google-cloud-python,jonparrott/gcloud-python,dhermes/gcloud-python,jonparrott/google-cloud-python,GoogleCloudPlatform/gcloud-python,tseaver/google-cloud-python,jonparrott/google-cloud-python,jonparrott/gcloud-python,tswast/google-cloud-python,tseaver/gcloud-python,tseaver/google-cloud-python,dhermes/google-cloud-python,GoogleCloudPlatform/gcloud-python,tseaver/google-cloud-python,dhermes/google-cloud-python