Fixing .drone

Signed-off-by: Jonas Franz <info@jonasfranz.software>

.drone.yml

@@ -23,6 +23,7 @@ pipeline:
     environment:
       GOPATH: /go
     commands:
+      - go get -u github.com/karalabe/xgo
       - xgo -out gg-migrator -ldflags "-X main.version=${DRONE_TAG##v} -X main.build=${DRONE_BUILD_NUMBER}" --targets=windows/*,darwin/*
     when:
       event: [ tag ]