Improve the description of refactor commit type

[YoPoulou]

In the git-z.toml file describing the different type of commit, the term refactor is defined as a tautology. Instead we could use a real definition. E.g. in wikipedia : "A code refactor is a proccess of restructuring existint source code without changing its external behavior".

Source : https://en.m.wikipedia.org/wiki/Code_refactoring

[ejpcmac]

I’m going for :

restructure the code without changing its external behaviour