Binder demo doesn't work

[lrzpellegrini]

• I have marked all applicable categories:
  • exception-raising bug
  • visual output bug
  • documentation request (i.e. "X is missing from the documentation." If instead I want to ask "how to use X?" I understand [StackOverflow#tqdm] is more appropriate)
  • new feature request
• I have visited the [source website], and in particular
  read the [known issues]
• I have searched through the [issue tracker] for duplicates
• I have mentioned version numbers, operating system and
  environment, where applicable

The Binder demo doesn't seem to work. I'm reaching Binder from the link in the README (https://mybinder.org/v2/gh/tqdm/tqdm/master?filepath=DEMO.ipynb).

Here is the error trace from Binder:

Waiting for build to start...
Picked Git content provider.
Cloning into '/tmp/repo2dockerj_cys6ji'...
HEAD is now at c58fc25 bump version, merge pull request #1112 from tqdm/devel
Using DockerBuildPack builder
Step 1/4 : FROM python:3.7-alpine
 ---> 72e4ef8abf8e
Step 2/4 : COPY dist/*.whl .
COPY failed: no source files were specified

The error applies to the c58fc25 commit (as reported in the trace).

[casperdcl]

fixed version for now (until #1113 is merged): https://mybinder.org/v2/gh/tqdm/tqdm/devel?filepath=DEMO.ipynb