fix task3 backend

deploy/task3/docker-compose.yml

@@ -1,6 +1,6 @@
 version: '3'
 services:
-  backend2:
+  backend3:
     build:
       dockerfile: ./task3-backend/Dockerfile
       context: ../..

go.mod

@@ -16,4 +16,5 @@ require (
 	github.com/sirupsen/logrus v1.4.2
 	github.com/spf13/viper v1.6.1
 	github.com/valyala/fasthttp v1.7.1
+	golang.org/x/sys v0.0.0-20191010194322-b09406accb47
 )

task3-backend/lib/server.go

@@ -305,7 +305,7 @@ func (s *Server) createLetter() (letterPath string, localFullPath string, err er
 		return
 	}
 
-	_ = unix.Sync()
+	unix.Sync()
 
 	return
 }