Fix RemoveStacktrace test to work with new sanitize_fields

Author: nateberkopec

spec/raven/processors/removestacktrace_spec.rb

@@ -4,6 +4,7 @@
 describe Raven::Processor::RemoveStacktrace do
   before do
     @client = double("client")
+    allow(@client).to receive_message_chain(:configuration, :sanitize_fields) { [] }
     @processor = Raven::Processor::RemoveStacktrace.new(@client)
   end