`trailing-whitespace`: exclude `tsv` files by default.

[randolf-scholz]

Tab separated values is a common data-format similar to .csv, but by definition uses tabs as the separator.

Trailing tab stops naturally occur when missing values are present, because each row needs to contain the same number of tabs. Hence, the trailing-whitespace hook can corrupt .tsv files. I propose to add exclude_types: [tsv] to the default configuration of the hook.

[asottile]

you can alwaysexclude_types in your own config

it's more surprising to make this choice for everyone here