fix shippable ci

shippable.yml

@@ -13,6 +13,7 @@ build:
     - curl -L -o golang.tar.gz https://dl.google.com/go/go1.10.3.linux-arm64.tar.gz
     - tar -C /usr/local -xzf golang.tar.gz
     - export PATH=$PATH:/usr/local/go/bin
+    - export GOPATH=/v2ray
     - go get -u v2ray.com/core/...
     - go get -u v2ray.com/ext/...
     - go test -p 1 -v v2ray.com/core/...