Hi!

I started to fix coding standards.
#3702

There are so many errors, I want to fix them.

Pros:

• It makes the code clean.
• We can get more contributors.
• It may find potential bugs.

Cons:

• It may introduce a new bug, we have to do it very carefully.
• We need hard work.

Actually, I did it for some files.
https://github.com/miya0001/wp-cli/commits/coding-standard

How do everybody think about it?