Fix lefthook config file
Our lefthook config file doesn't work on the latest Lefthook versions. It fails with:
$ lefthook version
1.1.1
$ lefthook install
Error: While parsing config: yaml: unmarshal errors:
line 4: mapping key "files" already defined at line 3
This MR fixes this issue by embedding commands into the relevant sections of the yaml file.
Edited by Dmitry Gruzd