Class name typo in the testing documentation

The section Watching ... from Probes references class TestKit where TestProbe should be used.
!act #3670: Removing old IO implementation
!act #3637: Add information about target in AskTimeout
Merge pull request #1779 from drewhk/wip-3670-remove-old-io-drewhk

!act #3670: Removing old IO implementation
Merge pull request #1780 from drewhk/wip-3637-friendlier-asktimeout-message-drewhk

!act #3637: Add information about target in AskTimeout
Merge pull request #1868 from decodeideas/master

Class name typo in the testing documentation
Merge remote-tracking branch: upstream/master