Fix a typo in the "first figure" tutorial (#606)

projection='M8i' sets the map width to 8 inch, not the figure width.
The figure with is larger than 8 inch, including frames and annotations.

examples/tutorials/first-figure.py

@@ -27,7 +27,7 @@
 ########################################################################################
 # Add elements to the figure using its methods. For example, let's start a map with an
 # automatic frame and ticks around a given longitude and latitude bound, set the
-# projection to Mercator (``M``), and the figure width to 8 inches:
+# projection to Mercator (``M``), and the map width to 8 inches:
 
 fig.basemap(region=[-90, -70, 0, 20], projection="M8i", frame=True)