Use conda-forge's blas package w/openblas

As conda-forge does not use the `nomkl` package, but instead uses the
`blas` package to select BLAS versions, install the `blas` package and
select the `openblas` implementation.

scipy-notebook/Dockerfile

@@ -18,7 +18,7 @@ USER $NB_UID
 # Remove pyqt and qt pulled in for matplotlib since we're only ever going to
 # use notebook-friendly backends in these images
 RUN conda install --quiet --yes \
-    'nomkl' \
+    'blas=*=openblas' \
     'ipywidgets=7.1*' \
     'pandas=0.19*' \
     'numexpr=2.6*' \