plot_ly tests don't need to run core.

They have the same dependencies as core. The optional
test jobs run the core tests because they have a different set of
dependencies

Author: jonmmease

tox.ini

@@ -135,19 +135,16 @@ commands=
 basepython={env:PLOTLY_TOX_PYTHON_27:}
 commands=
     python --version
-    nosetests {posargs} -x plotly/tests/test_core
     nosetests {posargs} -x plotly/tests/test_plot_ly
 
 [testenv:py34-plot_ly]
 basepython={env:PLOTLY_TOX_PYTHON_34:}
 commands=
     python --version
-    nosetests {posargs} -x plotly/tests/test_core
     nosetests {posargs} -x plotly/tests/test_plot_ly
 
 [testenv:py37-plot_ly]
 basepython={env:PLOTLY_TOX_PYTHON_37:}
 commands=
     python --version
-    nosetests {posargs} -x plotly/tests/test_core
     nosetests {posargs} -x plotly/tests/test_plot_ly