hook: Make go vet run all tests and fix warnings

hooks/pre-commit

@@ -4,6 +4,6 @@ set -eu
 
 golint src/...
 go fmt ./src/...
-go tool vet --shadow ./src
+go tool vet --all --shadow ./src
 gocyclo -over 12 src/
 gb test

src/github.com/matrix-org/dendrite/cmd/syncserver-integration-tests/main.go

@@ -286,7 +286,7 @@ func testSyncServer(syncServerCmdChan chan error, userID, since, want string) {
 		if err != nil {
 			fmt.Println("=============================================================================================")
 			fmt.Println("sync server failed to run. If failing with 'pq: password authentication failed for user' try:")
-			fmt.Println("    export PGHOST=/var/run/postgresql\n")
+			fmt.Println("    export PGHOST=/var/run/postgresql")
 			fmt.Println("=============================================================================================")
 			panic(err)
 		}