GitHub+Travis: update to latest golang patch version

.github/workflows/main.yml

@@ -18,6 +18,12 @@ env:
   GOPATH: /home/runner/work/go
   DOWNLOAD_CACHE: /home/runner/work/download_cache
   BITCOIN_VERSION: 0.20.1
+
+  # If you change this value, please change it in the following files as well:
+  # /.travis.yml
+  # /Dockerfile
+  # /dev.Dockerfile
+  # /.github/workflows/release.yml
   GO_VERSION: 1.15.6
 
 jobs:

.github/workflows/release.yaml

@@ -12,7 +12,13 @@ defaults:
 env:
   DOCKER_REPO: lightninglabs
   DOCKER_IMAGE: lnd
-  GO_VERSION: 1.15.5
+  
+  # If you change this value, please change it in the following files as well:
+  # /.travis.yml
+  # /Dockerfile
+  # /dev.Dockerfile
+  # /.github/workflows/main.yml
+  GO_VERSION: 1.15.6
 
 jobs:
   main:

.travis.yml

@@ -16,7 +16,12 @@ git:
   depth: false
 
 go:
-  - "1.15.x"
+  # If you change this value, please change it in the following files as well:
+  # /Dockerfile
+  # /dev.Dockerfile
+  # /.github/workflows/main.yml
+  # /.github/workflows/release.yml
+  - "1.15.6"
 
 env:
   global: