The proof corrections supplied by the author were not made to the final version of the article (Guarnizo, Amendola, Kunz and Vollmer, 2015).
We apologise to the authors and to the readers for this omission.
After (2.6) on page 348, the statement “being S = AR.” should read
“being S = AR. and P1 = R/A.”
Improved versions of the figures are also presented below.