Fix some typos in pipeline exception descriptions
Fix some typos in pipeline exception descriptions

linus-sherrill/sprokit,linus-sherrill/sprokit,linus-sherrill/sprokit,mathstuf/sprokit,Kitware/sprokit,Kitware/sprokit,mathstuf/sprokit,Kitware/sprokit,mathstuf/sprokit,linus-sherrill/sprokit,mathstuf/sprokit,Kitware/sprokit