upgrade Go to 1.15

Signed-off-by: Akihiro Suda <akihiro.suda.cz@hco.ntt.co.jp>

.travis.yml

@@ -2,19 +2,19 @@ dist: bionic
 language: go
 os: linux
 go:
+  - 1.15.x
   - 1.14.x
-  - 1.13.x
   - tip
 cache:
   directories:
   - /home/travis/.vagrant.d/boxes
 jobs:
   include:
-    - go: 1.14.x
+    - go: 1.15.x
       name: "verify-dependencies"
       script:
         - make verify-dependencies
-    - go: 1.13.x
+    - go: 1.15.x
       name: "cgroup-systemd"
       env:
         - RUNC_USE_SYSTEMD=1

Dockerfile

@@ -1,4 +1,4 @@
-ARG GO_VERSION=1.13
+ARG GO_VERSION=1.15
 ARG BATS_VERSION=v1.2.0
 ARG CRIU_VERSION=v3.14
 

Vagrantfile.centos7

@@ -15,7 +15,7 @@ Vagrant.configure("2") do |config|
     set -e -u -o pipefail
 
     # configuration
-    GO_VERSION="1.13.11"
+    GO_VERSION="1.15"
     BATS_VERSION="v1.2.0"
 
     # install yum packages