fix syntax error in package_overview example

Author: wholmgren

docs/sphinx/source/package_overview.rst

@@ -91,7 +91,7 @@ to accomplish our system modeling goal:
         pressure = pvlib.atmosphere.alt2pres(altitude)
         am_abs = pvlib.atmosphere.absoluteairmass(airmass, pressure)
         tl = pvlib.clearsky.lookup_linke_turbidity(times, latitude, longitude)
-        cs = pvlib.clearsky.ineichen(solpos['apparent_zenith', am_abs, tl,
+        cs = pvlib.clearsky.ineichen(solpos['apparent_zenith'], am_abs, tl,
                                      dni_extra=dni_extra, altitude=altitude)
         aoi = pvlib.irradiance.aoi(system['surface_tilt'], system['surface_azimuth'],
                                    solpos['apparent_zenith'], solpos['azimuth'])