trim spaces on left

[Farkal]

I think you should trim space on the left for each line.
I was trying to use efm with standard and here are the kind of output I got:

> standard -v /Users/me/Documents/prj/my-api/lib/app.js: 
standard: Use JavaScript Standard Style (https://standardjs.com)
standard: Run `standard --fix` to automatically fix some problems.
  /Users/me/Documents/prj/my-api/lib/app.js:4:1: Expected indentation of 2 spaces but found 8. (indent)
  /Users/me/Documents/prj/my-api/lib/app.js:5:1: Expected indentation of 4 spaces but found 2. (indent)
  /Users/me/Documents/prj/my-api/lib/app.js:6:1: Expected indentation of 2 spaces but found 4. (indent)
  /Users/me/Documents/prj/my-api/lib/app.js:8:1: Expected indentation of 2 spaces but found 4. (indent)

The linter only work if you use " %f:%l:%c: %m" for lint-formats

It also could be an option from errorformat

If you could provide some troubleshooting process for this kind of bug or better debug logs (adding if the entry was valid) I think it could help a lot of people to debug their linter.
I can make a PR to tell people to try to parse their linter output with errorformat i you want (but i can't do much more cause i don't know go 😢 ).

[mattn]

Did you try %-G ?