fix gapminder dataset paths

_episodes/03-plotting.md

@@ -639,13 +639,13 @@ it is possible to plot data in a pandas `DataFrame` or `Series`
 directly from the object itself.
 By default, pandas uses Matplotlib to create these plots.
 
-To demonstrate this, we will borrow a dataset
+To demonstrate this, we will borrow [a dataset](../data/gapminder_all.csv)
 prepared by [Software Carpentry][swc-gapminder-data]
 containing data on GDP and population size from [Gapminder][gapminder].
 
 ~~~
 import pandas as pd
-gapminder = pd.read_csv('../data/gapminder_all.csv', index_col='country')
+gapminder = pd.read_csv('data/gapminder_all.csv', index_col='country')
 print(gapminder.head())
 ~~~
 {: .language-python }