Faster conda package installs

Hi @astrofrog,

Thanks for making this example. I use it with nway and other astro packages.

I learned today that the lines

- conda create --yes -n test python=$TRAVIS_PYTHON_VERSION
- source activate test
- conda install --yes numpy=$NUMPY scipy=$SCIPY astropy matplotlib pytest pip

can be simplified to

- conda create --yes -n test python=$TRAVIS_PYTHON_VERSION numpy=$NUMPY scipy=$SCIPY astropy matplotlib pytest pip
- source activate test

conda create already needs to install some packages, and allows specifying additional packages to install. Instead of resolving dependencies twice, this does it then only once, making the build faster.

Cheers,
Johannes

Locate the Travis CI configuration containing the conda create and conda install commands shown in the issue. Read the surrounding setup steps, combine the package arguments as described, and verify that the configuration still installs the listed dependencies and completes the build faster.

Written by the indexing model from the issue text.