fixed user agent version (#34)

Author: nik-solcast

src/Solcast/Clients/BaseClient.cs

@@ -29,7 +29,8 @@ private static string GetAssemblyVersion()
                 typeof(AssemblyInformationalVersionAttribute)
             );
 
-            return attribute?.InformationalVersion ?? "1.0.0";
+            var version = attribute?.InformationalVersion ?? "1.0.0";
+            return version.Split('+')[0];
         }
     }
 }