Merge pull request pyqtgraph#990 from ziqiangxu/patch-3

Fix typo

doc/source/mouse_interaction.rst

@@ -10,7 +10,7 @@ Most applications that use pyqtgraph's data visualization will generate widgets
 In pyqtgraph, most 2D visualizations follow the following mouse interaction:
 
 * Left button: Interacts with items in the scene (select/move objects, etc). If there are no movable objects under the mouse cursor, then dragging with the left button will pan the scene instead.
-* Right button drag: Scales the scene. Dragging left/right scales horizontally; dragging up/down scales vertically (although some scenes will have their x/y scales locked together). If there are x/y axes fisible in the scene, then right-dragging over the axis will _only_ affect that axis.
+* Right button drag: Scales the scene. Dragging left/right scales horizontally; dragging up/down scales vertically (although some scenes will have their x/y scales locked together). If there are x/y axes visible in the scene, then right-dragging over the axis will _only_ affect that axis.
 * Right button click: Clicking the right button in most cases will show a context menu with a variety of options depending on the object(s) under the mouse cursor. 
 * Middle button (or wheel) drag: Dragging the mouse with the wheel pressed down will always pan the scene (this is useful in instances where panning with the left button is prevented by other objects in the scene).
 * Wheel spin: Zooms the scene in and out.