ci: update to adapt latest change (#25)

Author: spacewander

.github/workflows/ci.yml

@@ -26,7 +26,7 @@ jobs:
 
       - name: Install
         run: |
-          wget https://raw.githubusercontent.com/api7/apisix-build-tools/master/build-apisix-openresty.sh
+          wget https://raw.githubusercontent.com/api7/apisix-build-tools/v2.2.1/build-apisix-openresty.sh
           chmod +x build-apisix-openresty.sh
           OR_PREFIX=$OPENRESTY_PREFIX ./build-apisix-openresty.sh latest