Remove '-s' flag from ldflags from the build

This retains the symbols (but still removes the dwarf info).
This increases the executable size by ~8% (test on my laptop):

$ go build -ldflags '-w' -o nats-server
-rwxrwxr-x 1 yzhao yzhao 11911273 Jul 28 15:52 nats-server

$ go build -ldflags '-s -w' -o nats-server
-rwxrwxr-x 1 yzhao yzhao 11128832 Jul 28 15:52 nats-server

Symbols are very useful during debugging. It would be great that if the
NATS team consider including symbols.

.goreleaser.yml

@@ -14,7 +14,7 @@ builds:
 - main: ./main.go
   binary: nats-server
   ldflags:
-    - -s -w -X github.com/nats-io/nats-server/server.gitCommit={{.ShortCommit}}
+    - -w -X github.com/nats-io/nats-server/server.gitCommit={{.ShortCommit}}
   env:
     - GO111MODULE=off
     - CGO_ENABLED=0