Fix lgtm warnings in quadsums.py.

[duncanhobbs]

This pull request addresses this lgtm alert.

[coveralls]

Coverage decreased (-0.001%) to 93.921% when pulling 75d30b6 on duncanhobbs:lgtm-warn-quadsums into b722605 on QuantEcon:master.

[mmcky]

thanks @duncanhobbs these are interesting suggestions by lgtm. I tend to prefer the np.sqrt reference to know which function I am using in location without looking at the top of the code but if lgtm wants this style I guess I am ok with that :-)

@oyamad do you have a preference here?

[oyamad]

@mmcky I am not sure if I understand which you prefer, but I prefer

import numpy as np
...
... np.sqrt(beta) ...

to

from numpy import sqrt
...
... sqrt(beta) ...

[mmcky]

Thanks @oyamad I prefer the first style as well.

It appears LGTM is recommending the second.

[mmcky]

Sorry @duncanhobbs and @oyamad I am being dyslexic here. These changes are great as they are using the preferred style np.sqrt