rename conda env file to work with binder

Author: adrn

.travis.yml

@@ -20,7 +20,7 @@ env:
         - ASTROPY_VERSION=stable
         - EVENT_TYPE='pull_request push'
 
-        - CONDA_ENVIRONMENT='conda-environment.yml'
+        - CONDA_ENVIRONMENT='environment.yml'
         - CONDA_DEPENDENCIES='jupyter ipython'
         - CONDA_CHANNELS='astropy-ci-extras astropy'
 
@@ -49,4 +49,3 @@ script:
    #   --output-path=docs/rst-tutorials
    #   --template=docs/_static/astropy.tpl
    - python scripts/convert.py tutorials/notebooks --exec-only -v
-