Change the minor version of go to 1.13 (#13015)

* Changed go minor version 12 -> 13

* REQUIREDGOVERSION set to 1.13.0

Makefile

@@ -59,7 +59,7 @@ LDFLAGS += -X "github.com/mattermost/mattermost-server/model.BuildEnterpriseRead
 GO_MAJOR_VERSION = $(shell $(GO) version | cut -c 14- | cut -d' ' -f1 | cut -d'.' -f1)
 GO_MINOR_VERSION = $(shell $(GO) version | cut -c 14- | cut -d' ' -f1 | cut -d'.' -f2)
 MINIMUM_SUPPORTED_GO_MAJOR_VERSION = 1
-MINIMUM_SUPPORTED_GO_MINOR_VERSION = 12
+MINIMUM_SUPPORTED_GO_MINOR_VERSION = 13
 GO_VERSION_VALIDATION_ERR_MSG = Golang version is not supported, please update to at least $(MINIMUM_SUPPORTED_GO_MAJOR_VERSION).$(MINIMUM_SUPPORTED_GO_MINOR_VERSION)
 
 # GOOS/GOARCH of the build host, used to determine whether we're cross-compiling or not