STY: Use `.astype`'s `copy` kwarg in `np.tri`

Replace an explicit type check with setting `copy=False` in call to `astype`.
Merge pull request #4750 from jaimefrio/tri-sty

STY: Use `.astype`'s `copy` kwarg in `np.tri`
Merge pull request #1 from numpy/master

merge
Merge pull request #1 from gabloe/master

merge