Fix for fields getting corrupt
Fix for fields getting corrupt

In some scenarios the fields object would get corrupt. Especially in multiple goroutines.

We cannot use native `append` as it actually modifies the original slice - in this scenario `e.fields` will get modified.

Here is a related SO article: http://stackoverflow.com/questions/35276022/unexpected-slice-append-behaviour which describes this behavior.
dtannen/log,apex/log