Fix bug in drawing multiple stocks
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1. Cause: the previous one will check wether the data of the stock is of
the length of 253; however, in some cases, yahoo api would not return
enough history data; thus when all return data is less then 253 days,
the chart will be empty;
2. Solution: remove the check is enough. Even though some stocks like
GOOG would only have 30 days of data, it's still ok to show on the
chart.
Merge pull request #73 from COSI236TA/wenbin

Fix bug in drawing multiple stocks