Incorrect T-Stats in FamaMacBeth.py
Small bug in the FamaMacBeth class at lines 105-106-- the printed form of the regression results gives the STD twice, rather than the t-stat:
<code>
std_beta = self._results['std_beta'][i]
t_stat = self._results['std_beta'][i]
</code>

Last one should be t_stat instead of std_beta the second time.
