Minor Documentation and Typo Fixes (#2481)

* Update pvfactors.py

* Update _fit_desoto_pvsyst_sandia.py

Author: leopardracer

pvlib/bifacial/pvfactors.py

@@ -1,6 +1,6 @@
 """
 The ``bifacial.pvfactors`` module contains functions for modeling back surface
-plane-of-array irradiance using an external implementaton of the pvfactors
+plane-of-array irradiance using an external implementation of the pvfactors
 model (either ``solarfactors`` or the original ``pvfactors``).
 """
 

pvlib/ivtools/sdm/_fit_desoto_pvsyst_sandia.py

@@ -267,7 +267,7 @@ def _update_io(voc, iph, io, rs, rsh, nnsvth):
     .. [1] PVLib MATLAB https://github.com/sandialabs/MATLAB_PV_LIB
     .. [2] C. Hansen, Parameter Estimation for Single Diode Models of
        Photovoltaic Modules, Sandia National Laboratories Report SAND2015-2065
-    .. [3] C. Hansen, Estimation of Parameteres for Single Diode Models using
+    .. [3] C. Hansen, Estimation of Parameters for Single Diode Models using
        Measured IV Curves, Proc. of the 39th IEEE PVSC, June 2013.
     """