update CIs to Go 1.8

.travis.yml

@@ -12,7 +12,7 @@ services:
 go:
   - 1.6.4
   - 1.7.5
-  - 1.8rc1
+  - 1.8
 
 # first part of the GOARCH workaround
 # setting the GOARCH directly doesn't work, since the value will be overwritten later

appveyor.yml

@@ -13,8 +13,8 @@ clone_folder: c:\gopath\src\github.com\lucas-clemente\quic-go
 
 install:
   - rmdir c:\go /s /q
-  - appveyor DownloadFile https://storage.googleapis.com/golang/go1.7.5.windows-amd64.zip
-  - 7z x go1.7.5.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
   - set PATH=%PATH%;%GOPATH%\bin\windows_%GOARCH%;%GOPATH%\bin
   - echo %PATH%
   - echo %GOPATH%