BUG: Remove the spare white space in Chapter 4 Wernecke94 reference
BUG: Remove the spare white space in Chapter 4 Wernecke94 reference

Remove the spare white space in the Wernecke94 reference used in `Chapter
4` `The Visualization Pipeline`, section `4.7 Programming Models`:
https://lorensen.github.io/VTKExamples/site/VTKBook/04Chapter4/#412-references

lorensen/VTKExamples,lorensen/VTKExamples,lorensen/VTKExamples,lorensen/VTKExamples,lorensen/VTKExamples,lorensen/VTKExamples,lorensen/VTKExamples