can't use tags in image names

[paleozogt]

Consider this DockerMake.yml:

"foo:bar":
    FROM: ubuntu:trusty

With DockerMake 0.8, it will build fine. However, with 0.9 it fails:

➜  docker-make --version
docker-make version 0.9.0
➜  docker-make "foo:bar"
Working directory: /home/apollo/Development/test
Copy cache directory: /tmp
READING DockerMake.yml

Requested images: foo:bar

==========================================================================================================================================================================================================================================
                                                                             STARTING BUILD for "foo:bar" (image definition "foo:bar" from ./DockerMake.yml)

* Step 1/1 for image foo:bar
  Building step foo:bar defined in ./DockerMake.yml
  --------------------------------------------------------------------------------   1.foo:bar.dmk:c6f3faab-43e9-476a-aa89-df4f6a22bd80: BUILD LOG   --------------------------------------------------------------------------------
FATAL ERROR: Docker build failure

   -------- Docker daemon output --------
'500 Server Error: Internal Server Error ("invalid reference format")'
   -------- Arguments to client.build --------
{   'buildargs': None,
    'decode': True,
    'dockerfile': None,
    'fileobj': <_io.BytesIO object at 0x7f1012e4b0a0>,
    'nocache': False,
    'path': None,
    'pull': False,
    'rm': True,
    'squash': False,
    'tag': '1.foo:bar.dmk:c6f3faab-43e9-476a-aa89-df4f6a22bd80'}
This dockerfile was written to dockerfile.fail