TUN-3612: Upgrade to Go 1.15.6

Dockerfile

@@ -1,7 +1,7 @@
 # use a builder image for building cloudflare
 ARG TARGET_GOOS
 ARG TARGET_GOARCH
-FROM golang:1.15.5 as builder
+FROM golang:1.15.6 as builder
 ENV GO111MODULE=on \
     CGO_ENABLED=0 \
     TARGET_GOOS=${TARGET_GOOS} \

cfsetup.yaml

@@ -1,4 +1,4 @@
-pinned_go: &pinned_go go=1.15.5-1
+pinned_go: &pinned_go go=1.15.6-1
 build_dir: &build_dir /cfsetup_build
 default-flavor: buster
 stretch: &stretch
@@ -248,8 +248,8 @@ centos-7:
       - https://dl.fedoraproject.org/pub/epel/epel-release-latest-7.noarch.rpm
     pre-cache:
       - yum install -y fakeroot
-      - wget https://golang.org/dl/go1.15.5.linux-amd64.tar.gz -P /tmp/
-      - tar -C /usr/local -xzf /tmp/go1.15.5.linux-amd64.tar.gz
+      - wget https://golang.org/dl/go1.15.6.linux-amd64.tar.gz -P /tmp/
+      - tar -C /usr/local -xzf /tmp/go1.15.6.linux-amd64.tar.gz
     post-cache:
       - export PATH=$PATH:/usr/local/go/bin
       - export GOOS=linux
@@ -260,8 +260,8 @@ centos-7:
     builddeps: *el7_builddeps
     pre-cache:
       - yum install -y fakeroot
-      - wget https://golang.org/dl/go1.15.5.linux-amd64.tar.gz -P /tmp/
-      - tar -C /usr/local -xzf /tmp/go1.15.5.linux-amd64.tar.gz
+      - wget https://golang.org/dl/go1.15.6.linux-amd64.tar.gz -P /tmp/
+      - tar -C /usr/local -xzf /tmp/go1.15.6.linux-amd64.tar.gz
     post-cache:
       - export PATH=$PATH:/usr/local/go/bin
       - export GOOS=linux

dev.Dockerfile

@@ -1,4 +1,4 @@
-FROM golang:1.15.5 as builder
+FROM golang:1.15.6 as builder
 ENV GO111MODULE=on \
     CGO_ENABLED=0
 WORKDIR /go/src/github.com/cloudflare/cloudflared/