chapter 7 has two readme.md files

[guozheng]

chapter 7 directory has two readme files: README.md and readme.md. This caused git to give the warning about colliding paths:

warning: the following paths have collided (e.g. case-sensitive paths
on a case-insensitive filesystem) and only one from the same
colliding group is in the working tree:

  'chapter07/README.md'
  'chapter07/readme.md'

These two files seem to have the same content, can we delete one of them?

[guozheng]

Also, the readme content says Chapter 9 instead of Chapter 7.