README, go.mod: require go 1.15+

This mostly reverts commit e2dd9220dd, and bumps
the min Go version to 1.15.

Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>

README.md

@@ -24,7 +24,7 @@ A third party security audit was performed by Cure53, you can see the full repor
 ## Building
 
 `runc` currently supports the Linux platform with various architecture support.
-It must be built with Go version 1.14 or higher.
+It must be built with Go version 1.15 or higher.
 
 In order to enable seccomp support you will need to install `libseccomp` on your platform.
 > e.g. `libseccomp-devel` for CentOS, or `libseccomp-dev` for Ubuntu

go.mod

@@ -1,6 +1,6 @@
 module github.com/opencontainers/runc
 
-go 1.13
+go 1.15
 
 require (
 	github.com/bits-and-blooms/bitset v1.2.0

vendor/modules.txt

@@ -1,9 +1,12 @@
 # github.com/bits-and-blooms/bitset v1.2.0
+## explicit
 github.com/bits-and-blooms/bitset
 # github.com/checkpoint-restore/go-criu/v5 v5.0.0
+## explicit
 github.com/checkpoint-restore/go-criu/v5
 github.com/checkpoint-restore/go-criu/v5/rpc
 # github.com/cilium/ebpf v0.6.2
+## explicit
 github.com/cilium/ebpf
 github.com/cilium/ebpf/asm
 github.com/cilium/ebpf/internal
@@ -11,27 +14,36 @@ github.com/cilium/ebpf/internal/btf
 github.com/cilium/ebpf/internal/unix
 github.com/cilium/ebpf/link
 # github.com/containerd/console v1.0.2
+## explicit
 github.com/containerd/console
 # github.com/coreos/go-systemd/v22 v22.3.2
+## explicit
 github.com/coreos/go-systemd/v22/activation
 github.com/coreos/go-systemd/v22/dbus
 # github.com/cpuguy83/go-md2man/v2 v2.0.0-20190314233015-f79a8a8ca69d
 github.com/cpuguy83/go-md2man/v2/md2man
 # github.com/cyphar/filepath-securejoin v0.2.3
+## explicit
 github.com/cyphar/filepath-securejoin
 # github.com/docker/go-units v0.4.0
+## explicit
 github.com/docker/go-units
 # github.com/godbus/dbus/v5 v5.0.4
+## explicit
 github.com/godbus/dbus/v5
 # github.com/golang/protobuf v1.5.0
 github.com/golang/protobuf/proto
 # github.com/moby/sys/mountinfo v0.4.1
+## explicit
 github.com/moby/sys/mountinfo
 # github.com/mrunalp/fileutils v0.5.0
+## explicit
 github.com/mrunalp/fileutils
 # github.com/opencontainers/runtime-spec v1.0.3-0.20210326190908-1c3f411f0417
+## explicit
 github.com/opencontainers/runtime-spec/specs-go
 # github.com/opencontainers/selinux v1.8.2
+## explicit
 github.com/opencontainers/selinux/go-selinux
 github.com/opencontainers/selinux/go-selinux/label
 github.com/opencontainers/selinux/pkg/pwalk
@@ -40,28 +52,36 @@ github.com/pkg/errors
 # github.com/russross/blackfriday/v2 v2.0.1
 github.com/russross/blackfriday/v2
 # github.com/seccomp/libseccomp-golang v0.9.1
+## explicit
 github.com/seccomp/libseccomp-golang
 # github.com/shurcooL/sanitized_anchor_name v1.0.0
 github.com/shurcooL/sanitized_anchor_name
 # github.com/sirupsen/logrus v1.8.1
+## explicit
 github.com/sirupsen/logrus
 github.com/sirupsen/logrus/hooks/test
 # github.com/syndtr/gocapability v0.0.0-20200815063812-42c35b437635
+## explicit
 github.com/syndtr/gocapability/capability
 # github.com/urfave/cli v1.22.1
+## explicit
 github.com/urfave/cli
 # github.com/vishvananda/netlink v1.1.0
+## explicit
 github.com/vishvananda/netlink
 github.com/vishvananda/netlink/nl
 # github.com/vishvananda/netns v0.0.0-20191106174202-0a2b9b5464df
 github.com/vishvananda/netns
 # golang.org/x/net v0.0.0-20201224014010-6772e930b67b
+## explicit
 golang.org/x/net/bpf
 # golang.org/x/sys v0.0.0-20210426230700-d19ff857e887
+## explicit
 golang.org/x/sys/internal/unsafeheader
 golang.org/x/sys/unix
 golang.org/x/sys/windows
 # google.golang.org/protobuf v1.27.1
+## explicit
 google.golang.org/protobuf/encoding/prototext
 google.golang.org/protobuf/encoding/protowire
 google.golang.org/protobuf/internal/descfmt