binary-update: Do not fetch update info for minio binary compiled from source.

fixes #2494

cmd/main.go

@@ -20,6 +20,7 @@ import (
 	"fmt"
 	"os"
 	"sort"
+	"strings"
 
 	"github.com/minio/cli"
 	"github.com/minio/mc/pkg/console"
@@ -180,14 +181,16 @@ func Main() {
 
 		// Do not print update messages, if quiet flag is set.
 		if !globalQuiet {
-			// Do not print any errors in release update function.
-			noError := true
-			updateMsg := getReleaseUpdate(minioUpdateStableURL, noError)
-			if updateMsg.Update {
+			if strings.HasPrefix(Version, "RELEASE.") {
+				updateMsg, _, err := getReleaseUpdate(minioUpdateStableURL)
+				if err != nil {
+					// Ignore any errors during getReleaseUpdate() because
+					// the internet might not be available.
+					return nil
+				}
 				console.Println(updateMsg)
 			}
 		}
-
 		return nil
 	}