add build args to drone pipeline

.drone.yml

@@ -10,6 +10,8 @@ steps:
 - name: dryrun
   image: plugins/docker:18-linux-amd64
   settings:
+    build_args:
+      MOLECULE_VERSION: ${DRONE_TAG%-*}
     dockerfile: Dockerfile
     dry_run: true
     password:
@@ -26,6 +28,8 @@ steps:
   settings:
     auto_tag: true
     auto_tag_suffix: amd64
+    build_args:
+      MOLECULE_VERSION: ${DRONE_TAG%-*}
     dockerfile: Dockerfile
     password:
       from_secret: docker_password
@@ -120,6 +124,6 @@ depends_on:
 
 ---
 kind: signature
-hmac: f0d15cc962a0fc24405a835ed125ce8af4769c0f4f7458c147b7cf612270c48c
+hmac: be9fd46c13479234356c404f031f5de5a7401accfa6ee6a0bdf1498f5b98c61f
 
 ...