Bump nuget to 2.0.0 RTM.

Author: angularsen

UnitsNet.nuspec

@@ -2,7 +2,7 @@
 <package xmlns="http://schemas.microsoft.com/packaging/2011/08/nuspec.xsd">
   <metadata>
     <id>UnitsNet</id>
-    <version>2.0.0-beta</version>
+    <version>2.0.0</version>
     <title>Units.NET</title>
     <authors>Andreas Gullberg Larsen</authors>
     <owners>Initial Force AS</owners>