[misc] Fixed a copy paste issue.

This PR corrects a copy paste issue in the README.md file.

Author: sean-gilliam

README.md

@@ -1,4 +1,4 @@
-#### Akka.Logger.Serilog ####
+#### Akka.Logger.log4net ####
 
 This is the log4net integration plugin for Akka.NET. Please check out our [documentation](http://getakka.net/docs/Logging) for examples on how to configure your custom logger plugin for usage.
-Currently targetting Log4Net 2.0.5
+Currently targetting Log4Net 2.0.5