Update news and version

DESCRIPTION

 Package: stressaddition
 Type: Package
 Title: Modeling Tri-Phasic Concentration-Response Relationships
-Version: 2.0.0
+Version: 2.0.0.9000
 Date: 2020-02-17
 Authors@R: person("Sebastian", "Henz", role = c("aut", "cre"), 
                   email = "sebastian.henz@ufz.de", 

NEWS.md

+# stressaddition (development version)
+
+* Fix documentation of `ecxsys()` and `predict_ecxsys`.
+
 # stressaddition 2.0.0
 
 * Changed the order of arguments in `ecxsys()`.