Print correct line numbers for warnings.
Print correct line numbers for warnings.

That is, print something like:
  ... apache_beam/io/gcp/pubsub_test.py:72: DeprecationWarning: ...
instead of:
  ... apache_beam/utils/annotations.py:99: DeprecationWarning:  ...

charlesccychen/incubator-beam,RyanSkraba/beam,apache/beam,lukecwik/incubator-beam,tgroh/beam,robertwb/incubator-beam,apache/beam,lukecwik/incubator-beam,RyanSkraba/beam,RyanSkraba/beam,RyanSkraba/beam,robertwb/incubator-beam,chamikaramj/beam,apache/beam,apache/beam,chamikaramj/beam,RyanSkraba/beam,rangadi/beam,lukecwik/incubator-beam,iemejia/incubator-beam,charlesccychen/beam,rangadi/beam,markflyhigh/incubator-beam,chamikaramj/beam,apache/beam,chamikaramj/beam,charlesccychen/beam,rangadi/beam,markflyhigh/incubator-beam,tgroh/beam,charlesccychen/beam,markflyhigh/incubator-beam,apache/beam,charlesccychen/incubator-beam,apache/beam,apache/beam,markflyhigh/incubator-beam,rangadi/beam,tgroh/incubator-beam,lukecwik/incubator-beam,charlesccychen/beam,apache/beam,chamikaramj/beam,iemejia/incubator-beam,tgroh/beam,robertwb/incubator-beam,lukecwik/incubator-beam,chamikaramj/beam,robertwb/incubator-beam,rangadi/incubator-beam,rangadi/incubator-beam,RyanSkraba/beam,chamikaramj/beam,apache/beam,chamikaramj/beam,robertwb/incubator-beam,lukecwik/incubator-beam,apache/beam,lukecwik/incubator-beam,rangadi/incubator-beam,charlesccychen/incubator-beam,charlesccychen/beam,rangadi/beam,lukecwik/incubator-beam,markflyhigh/incubator-beam,robertwb/incubator-beam,lukecwik/incubator-beam,charlesccychen/beam,rangadi/beam,robertwb/incubator-beam,robertwb/incubator-beam,mxm/incubator-beam,tgroh/incubator-beam,markflyhigh/incubator-beam,RyanSkraba/beam,chamikaramj/beam,lukecwik/incubator-beam,chamikaramj/beam,markflyhigh/incubator-beam,robertwb/incubator-beam,robertwb/incubator-beam,rangadi/beam,mxm/incubator-beam,tgroh/beam,charlesccychen/beam