Fix go1.11 vet shadow errors (#6555)

cmd/admin-handlers.go

@@ -675,7 +675,7 @@ func (a adminAPIHandlers) GetConfigKeysHandler(w http.ResponseWriter, r *http.Re
 			continue
 		}
 		val := gjson.Get(configStr, key)
-		if j, err := sjson.Set(newConfigStr, normalizeJSONKey(key), val.Value()); err == nil {
+		if j, ierr := sjson.Set(newConfigStr, normalizeJSONKey(key), val.Value()); ierr == nil {
 			newConfigStr = j
 		}
 	}

cmd/common-main.go

@@ -161,7 +161,7 @@ func handleCommonEnvVars() {
 
 	globalDomainName, globalIsEnvDomainName = os.LookupEnv("MINIO_DOMAIN")
 	if globalDomainName != "" {
-		if _, ok := dns2.IsDomainName(globalDomainName); !ok {
+		if _, ok = dns2.IsDomainName(globalDomainName); !ok {
 			logger.Fatal(uiErrInvalidDomainValue(nil).Msg("Unknown value `%s`", globalDomainName), "Invalid MINIO_DOMAIN environment variable")
 		}
 	}