Fix test to match exercise description.

[rhwood]

Assuming that I am interpreting the Bob exercise description correctly, this will fix #521.

Fixes #521

[ErikSchierboom]

@rhwood This is basically the same PR as https://github.com/exercism/swift/pull/507, but with the exemplar solution updated. Usually, we give precendence to earlier PRs when merging. @Ryan-Gross1993 were you planning on updating #507?

[rhwood]

I submitted this and only afterwards discovered that #507 covered the same problem.

[ErikSchierboom]

@rhwood I totally understand. It's an easy enough mistake :) I'll let Ryan reply, and then we'll see which PR to merge.