[BUG] Make Benchmark tz-aware
[BUG] Make Benchmark tz-aware

This is a one line change that makes get_data_from_yahoo return
a timezone aware series (UTC).

Once the benchmark file gets overwritten the h5 file will have the
timezone so this should fix any benchmark timezone issues for
people using pyfolio locally.

YihaoLu/pyfolio,sketchytechky/pyfolio,r0k3/pyfolio,quantopian/pyfolio,sketchytechky/pyfolio,dursk/pyfolio,yanheven/pyfolio,dursk/pyfolio,raybuhr/pyfolio,yanheven/pyfolio,YihaoLu/pyfolio,ChinaQuants/pyfolio,ChinaQuants/pyfolio,femtotrader/pyfolio,quantopian/pyfolio,raybuhr/pyfolio,chayapan/pyfolio,r0k3/pyfolio,femtotrader/pyfolio