Fix update version to use the appropriate rc style for C#

update_version.py

@@ -155,13 +155,13 @@ def UpdateCsharp():
   RewriteXml('csharp/src/Google.Protobuf/Google.Protobuf.csproj',
     lambda document : ReplaceText(
       Find(Find(document.documentElement, 'PropertyGroup'), 'VersionPrefix'),
-      GetFullVersion(rc_suffix = '-rc.')),
+      GetFullVersion(rc_suffix = '-rc')),
     add_xml_prefix=False)
 
   RewriteXml('csharp/Google.Protobuf.Tools.nuspec',
     lambda document : ReplaceText(
       Find(Find(document.documentElement, 'metadata'), 'version'),
-      GetFullVersion(rc_suffix = '-rc.')))
+      GetFullVersion(rc_suffix = '-rc')))
 
 
 def UpdateJava():