Fix typo in tools.py
perfrom -> perform
@@ -237,7 +237,7 @@ class Tap(GestureTool):
@abstract
class SelectTool(GestureTool):
- ''' A base class for tools that perfrom "selections", e.g. ``BoxSelectTool``.
+ ''' A base class for tools that perform "selections", e.g. ``BoxSelectTool``.
'''
