Move "lints" package to dev_dependencies

[erf]

I wanted to try out this package but i got a dependency problem with flutter_lints:

Because no versions of flutter_lints match >2.0.1 <3.0.0 and flutter_lints 2.0.1 depends on lints ^2.0.0, flutter_lints ^2.0.1 requires lints ^2.0.0.
And because every version of dart_git from git depends on lints ^1.0.1, flutter_lints ^2.0.1 is incompatible with dart_git from git.
So, because kanban depends on both dart_git from git and flutter_lints ^2.0.1, version solving failed.
pub get failed (1; So, because kanban depends on both dart_git from git and flutter_lints ^2.0.1, version solving failed.)
exit code 1

I think this could be solved by moving lints to dev_dependencies