standardize optional requirements for CircleCI

- add coverage to optional requirements
- pip install optional requirements and no need for
  nothing else

Author: etpinard

optional-requirements.txt

@@ -12,10 +12,11 @@ numpy
 # matplotlib==1.3.1
 
 ## testing dependencies ##
-nose==1.3.3
+nose
+coverage
 
-## ipython dependencies ##
-ipython[all]==3.0.0
+## ipython ##
+ipython
 
 ## pandas deps for some matplotlib functionality ##
 pandas