CI: Update Travis config
CI: Update Travis config

 * Let it include the deploy stage only when the commit has a tag.
 * This makes untagged commits to skip the deploy job entirely
   (it even does not show up in the Travis' build job status page)
   so everyday testing will finish a little faster.

barrachri/aiodocker,paultag/aiodocker,gaopeiliang/aiodocker,gaopeiliang/aiodocker,gaopeiliang/aiodocker,barrachri/aiodocker,barrachri/aiodocker