Update pvlib/clearsky.py

Co-authored-by: Anton Driesse <anton.driesse@pvperformancelabs.com>

Author: cwhanse

pvlib/clearsky.py

@@ -22,7 +22,7 @@ def ineichen(apparent_zenith, airmass_absolute, linke_turbidity,
     Determine clear-sky GHI, DNI, and DHI using the Ineichen/Perez model.
 
     The Ineichen and Perez clear sky model [1]_ [2]_ describes global
-    horizontal irradiance (GHI) and direct normal irradiance (DNI), Diffuse
+    horizontal irradiance (GHI) and direct normal irradiance (DNI). Diffuse
     horizontal irradiance (DHI) is then computed as DHI = GHI - DNI*cos(zenith)
     Analysis of clear sky models found the Ineichen/Perez model to have
     excellent performance with a minimal input data set [3]_.