Use Go 1.16 in GitHub actions workflows

Author: artyom

.github/workflows/docker.yml

@@ -14,7 +14,7 @@ jobs:
     steps:
     - uses: actions/setup-go@v1
       with:
-        go-version: '1.15.x'
+        go-version: '1.16.x'
     - uses: actions/checkout@v1
     - name: Get dependencies
       run: go mod download

.github/workflows/release.yml

@@ -10,7 +10,7 @@ jobs:
     steps:
     - uses: actions/setup-go@v1
       with:
-        go-version: '1.15.x'
+        go-version: '1.16.x'
     - uses: actions/checkout@v1
     - name: Get dependencies
       run: go mod download

.github/workflows/test.yml

@@ -7,7 +7,7 @@ jobs:
     steps:
     - uses: actions/setup-go@v1
       with:
-        go-version: '1.15.x'
+        go-version: '1.16.x'
     - uses: actions/checkout@v1
     - name: Get dependencies
       run: go mod download