Revert "go: update to 1.16 (#1657)" (#1855)

This reverts commit 17f7837b.

.github/workflows/go.yml

@@ -14,7 +14,7 @@ jobs:
     runs-on: ${{ matrix.os }}
     strategy:
       matrix:
-        go: [1.16]
+        go: [1.15]
         os: [ubuntu-latest, macos-latest, windows-latest]
     steps:
     - name: Setup Go

.github/workflows/release.yaml

@@ -14,7 +14,7 @@ jobs:
       - name: Setup Go
         uses: actions/setup-go@v2
         with:
-          go-version: 1.16
+          go-version: 1.15
       - name: Checkout
         uses: actions/checkout@v2
         with:

Dockerfile

-FROM golang:1.16 AS build
+FROM golang:1.15 AS build
 
 WORKDIR /src
 # enable modules caching in separate layer

go.mod

 module github.com/ethersphere/bee
 
-go 1.16
+go 1.15
 
 require (
 	github.com/btcsuite/btcd v0.21.0-beta