Update dplyr.Rmd

[MPK2014]

Dear Roger, I love learning from you. If I may suggest a change, I would explain %>% a bit more (see the code). And preferably place it before all functions, so it can directly be rehearsed when new functions (select, filter etc.) are introduced.

[MPK2014]

Im not sure how GitHub works and if you get this comment, but one more time, thank you for your contribution in teaching data science and I added some suggestions to the book Exprloring Data Analysis about dplyr chatper and the %>% operator.