Some more examples updated to use matplotlib.pyplot
Modified example 'plot_stock_market.py' to use matplotlib.pyplot

Modified despite #3153 because
- Error is not related to pylab or matplotlib.pyplot
- Removing the symbol 'DELL' from the example solves the problem
Merge pull request #3154 from rajatkhanduja/fixing_examples

[MRG+1] Updated remaining examples to use pyplot for plotting instead of pylab