assorted basic and hopefully uncontroversial changes

The first commit is simply spelling corrections.

The second doesn't really involve coding, just deciding whether my wording actually makes the error message clearer.

The last commit should also be straightforward, unless a fan of grunt-4 wants to start a debate about which images to use. (However, if Ivanovic suddenly puts out 1.11.5, a reference will have to be changed to "after 1.11.5" or "before 1.11.6"!)