[release/1.4] update Go 1.15.5 (to match containerd)

Changes: https://golang.org/doc/devel/release.html#go1.15

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

.appveyor.yml

@@ -10,7 +10,7 @@ environment:
   CGO_ENABLED: 1
   GO111MODULE: off
   matrix:
-    - GO_VERSION: 1.13.15
+    - GO_VERSION: 1.15.5
 
 install:
   # Install Mingw

.github/workflows/ci.yml

@@ -14,7 +14,7 @@ jobs:
       - name: Install Go
         uses: actions/setup-go@v1
         with:
-          go-version: '1.13.15'
+          go-version: '1.15.5'
 
       - name: Set env
         shell: bash
@@ -82,7 +82,7 @@ jobs:
       - name: Install Go
         uses: actions/setup-go@v1
         with:
-          go-version: '1.13.15'
+          go-version: '1.15.5'
 
       - name: Set env
         shell: bash
@@ -147,10 +147,10 @@ jobs:
     name: Build and CRI Test (Windows amd64)
     runs-on: windows-2016
     steps:
-      - name: Set up Go 1.13.15
+      - name: Set up Go 1.15.5
         uses: actions/setup-go@v1
         with:
-          go-version: 1.13.15
+          go-version: 1.15.5
 
       - name: Checkout cri repo
         uses: actions/checkout@v2

README.md

@@ -88,7 +88,7 @@ specifications as appropriate.
 backport version of `libseccomp-dev` is required. See [travis.yml](.travis.yml) for an example on trusty.
 * **btrfs development library.** Required by containerd btrfs support. `btrfs-tools`(Ubuntu, Debian) / `btrfs-progs-devel`(Fedora, CentOS, RHEL)
 2. Install **`pkg-config`** (required for linking with `libseccomp`).
-3. Install and setup a Go 1.13.15 development environment.
+3. Install and setup a Go 1.15.5 development environment.
 4. Make a local clone of this repository.
 5. Install binary dependencies by running the following command from your cloned `cri/` project directory:
 ```bash