update signature of static warning

[ChrisBeaumont]

The static_warning method doesn't give it's helpful error message if keyword parameters are supplied:

In [1]: from astrodendro.dendrogram import Dendrogram
In [2]: d = Dendrogram()
In [3]: d.compute('test.fits', min_flux=2)
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-3-2f4ec08a4ef3> in <module>()
----> 1 d.compute('test.fits', min_flux=2)

TypeError: static_warning() got an unexpected keyword argument 'min_flux'

This PR makes sure the static warning message is always displayed

[astrofrog]

Looks good, feel free to merge!