[ci] set gopath to under ci project dir

.gitlab-ci.yml

@@ -81,8 +81,8 @@ osx_installer:
   stage: build
   allow_failure: true
   variables:
-      GOPATH: ~/go/
-      APP_PATH: ~/go/src/0xacab.org/leap/bitmask-systray
+      GOPATH: $CI_PROJECT_DIR/go/
+      APP_PATH: $CI_PROJECT_DIR/go/src/0xacab.org/leap/bitmask-systray
   script:
     - git clone https://0xacab.org/leap/riseup_vpn
     - cd riseup_vpn