fix(server.go) fix data race between func LogEntries and func appendEntry
The append function in appendEntry might change the value of the slice pointer when it wants to grow the capacity of the slice. We are not protecting the content of the slice, since the LogEntries func is just used for internal testing. The main reason of this pull request is to make the race detector happy during the testing.
Merge pull request #217 from xiangli-cmu/fix_data_race

fix(server.go) fix data race between func LogEntries and func appendEntry