update tutorial and fix coding style

Author: chfw

docs/source/tutorial01.rst

@@ -113,6 +113,6 @@ We got a perfect data table. Let us draw it to a svg file:
 
 .. code-block:: python
 
-    >>> svg = sheet.save_to_memory(file_type='svg', chart_type='line',
+    >>> sheet.save_as("life_expectancy_in_brics_countries.svg", chart_type='line',
     ...     title='Life expectancy at birth in BRICS countries (years)',
-    ...     x_labels_major_count=10, x_label_rotation=30, show_minor_x_labels=False)#"life_expectancy_in_brics_countries.svg"
+    ...     x_labels_major_count=10, x_label_rotation=30, show_minor_x_labels=False)

pyexcel_chart/__init__.py

@@ -185,8 +185,10 @@ def __init__(self, file_type):
 
     def get_io(self):
         io = BytesIO()
+
         def repr_svg(self):
             return self.getvalue().decode('utf-8')
+
         io._repr_svg_ = partial(repr_svg, io)
         return io