Update NLogLogger.cs

Fix wrapper so we can get the original method that caused the logger to log. (${callsite})

See:
http://stackoverflow.com/questions/7412156/how-to-retain-callsite-information-when-wrapping-nlog
http://stackoverflow.com/questions/5132759/nlog-callsite-information
Merge pull request #2 from morindo/patch-1

Update NLogLogger.cs