Fix the deployment step in Travis (#47)

Publishing to PyPI (when there's a git tag) was failing because pip install attrs>=19 produced
and artifact file; which in turn makes flit build complain.

* add some debug steps to the travis pipeline

* remove unused files

* fix install of latest attrs version

* only install flit in deployment stage

* re-instate normal tests and publish step

.travis.yml

@@ -16,12 +16,13 @@ script:
   - find docs -name '*.ipynb' -maxdepth 2 | xargs jupyter nbconvert --to notebook --execute
   # submit coverage report to coveralls
   - python -m coveralls
+  # - ls -la
 install:
   - pip install --upgrade -qq pip flit
   - flit install --symlink --extras=test,examples
   # - pip install --upgrade -q '.[test,examples]'
   # seems to be required for this not to break??
-  - pip install --upgrade -qq attrs>=19.3.0
+  - pip install --upgrade -qq 'attrs>=19.3.0'
 jobs:
   include:
     - stage: "Static code analysis"
@@ -48,6 +49,8 @@ jobs:
     - stage: deploy
       name: "Deploy to pypi"
       if: tag IS present
+      install:
+        - pip install flit
       script:
         - flit build
         - env FLIT_USERNAME=$PYPI_USER FLIT_PASSWORD=$PYPI_PASSWORD flit publish