Changed description reference in CloudStateLevel

Changed the reference to wikipedia from german to english. There was a problem with the german "oe" in the link.

Signed-off-by: Markus Waldmann <Markus.Waldmann@stud.hs-kempten.de>

Author: Markus Waldmann

osi_environment.proto

@@ -368,7 +368,7 @@ message EnvironmentalConditions
         //
         // \par References:
         // [1] ISO 15469:2004(E) / CIE S 011/E:2003 : Spatial distribution of skylight
-        // [2] https://de.wikipedia.org/wiki/Bewölkung
+        // [2] https://en.wikipedia.org/wiki/Cloud_cover
         // [3] https://www.dwd.de/DE/service/lexikon/Functions/glossar.html?lv2=100932&lv3=101016
         //
         enum CloudStateLevel