Show infos when using dart_analyze linter

[grlduarte]

Currently the infos are not showed by ALE when working with Dart files.

• Changed the linter command to use the argument --fatal-infos so that when there's one info it triggers ALE,
• Updated the test routine.

Code snippet for testing:

// main.dart
class A {
  const A();
}

void accessA() {
  A a = new A();
}

[hsanson]

I think these changes should not affect the already exising tests. Please keep the previous tests and add the new ones.

[grlduarte]

Done. Just had to remove the whitespaces before the warning message in the existing test. It seems now that the output right justifies the severity codes:

  error - main.dart:9:1 - Expected to find '}'. - expected_token
warning - main.dart:2:11 - The receiver can't be null, so the null-aware operator '?.' is unnecessary. Try replacing the operator '?.' with '.'. - invalid_null_aware_operator
   info - main.dart:8:3 - Dead code. Try removing the code, or fixing the code before it so that it can be reached. - d
ead_code

[hsanson]

Looks good, thanks.