DOC: Updates README.rst with svg badges (#2771)

README.rst

@@ -136,11 +136,11 @@ Feel free to ask questions on the `mailing list <https://groups.google.com/forum
    :target: https://gitter.im/quantopian/zipline?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge
 .. |version status| image:: https://img.shields.io/pypi/pyversions/zipline.svg
    :target: https://pypi.python.org/pypi/zipline
-.. |travis status| image:: https://travis-ci.org/quantopian/zipline.png?branch=master
+.. |travis status| image:: https://travis-ci.org/quantopian/zipline.svg?branch=master
    :target: https://travis-ci.org/quantopian/zipline
 .. |appveyor status| image:: https://ci.appveyor.com/api/projects/status/3dg18e6227dvstw6/branch/master?svg=true
    :target: https://ci.appveyor.com/project/quantopian/zipline/branch/master
-.. |Coverage Status| image:: https://coveralls.io/repos/quantopian/zipline/badge.png
+.. |Coverage Status| image:: https://coveralls.io/repos/quantopian/zipline/badge.svg
    :target: https://coveralls.io/r/quantopian/zipline
 
 .. _`Zipline Install Documentation` : https://www.zipline.io/install