Rewrite docstring more in line with the others

Author: berland

Lib/shutil.py

@@ -68,7 +68,7 @@ class Error(OSError):
     pass
 
 class ErrorGroup(Error):
-    """Used when gathering multiple exceptions"""
+    """Raised when multiple exceptions have been caught"""
 
 class SameFileError(Error):
     """Raised when source and destination are the same file."""