Fixe the broken image link in the README.md

Renamed the Sample Jupyter Graph image file, removed the spaces between
the words. Used the camel case. Updated the new changed name in the
README.d, and now the README.md is processed correctly.

README.md

@@ -7,7 +7,7 @@ A Google Charts API for Python 2 and 3, meant to be used as an alternative to ma
 
 ## Jupyter Screenshot
 
-![Alt text](assets/Sample\ Jupyter\ graph.png?raw=true "Jupyter example")
+![Alt text](assets/SampleJupyterGraph.png?raw=true "Jupyter example")
 
 You can find a Jupyter notebook with examples [here](examples/gpcharts%20test.ipynb). A Python script with examples can be found [here](examples/testGraph.py).