Update CI to use Go 1.8 (#1444)

.travis.yml

 language: go
 
 go:
-  - 1.7.4
+  - 1.8
   - tip
 
 matrix:

README.md

@@ -99,7 +99,7 @@ the [CLI documentation](https://caddyserver.com/docs/cli) for details.
 
 ## Running from Source
 
-Note: You will need **[Go 1.7](https://golang.org/dl/)** or newer.
+Note: You will need **[Go 1.8](https://golang.org/dl/)** or newer.
 
 1. `go get github.com/mholt/caddy/caddy`
 2. `cd` into your website's directory

appveyor.yml

@@ -9,8 +9,8 @@ environment:
 
 install:
   - rmdir c:\go /s /q
-  - appveyor DownloadFile https://storage.googleapis.com/golang/go1.7.4.windows-amd64.zip
-  - 7z x go1.7.4.windows-amd64.zip -y -oC:\ > NUL
+  - appveyor DownloadFile https://storage.googleapis.com/golang/go1.8.windows-amd64.zip
+  - 7z x go1.8.windows-amd64.zip -y -oC:\ > NUL
   - go version
   - go env
   - go get -t ./...