Fixes linter warnings (#3021)

Author: themisir

lib/src/command/add.dart

@@ -5,7 +5,6 @@
 // @dart=2.10
 
 import 'package:path/path.dart' as p;
-import 'package:pub/src/source/path.dart';
 import 'package:pub_semver/pub_semver.dart';
 import 'package:yaml/yaml.dart';
 
@@ -19,6 +18,7 @@ import '../package.dart';
 import '../package_name.dart';
 import '../pubspec.dart';
 import '../solver.dart';
+import '../source/path.dart';
 import '../utils.dart';
 import '../yaml_edit/editor.dart';
 

lib/src/global_packages.dart

@@ -22,8 +22,8 @@ import 'package.dart';
 import 'package_name.dart';
 import 'pubspec.dart';
 import 'sdk.dart';
-import 'solver/incompatibility_cause.dart';
 import 'solver.dart';
+import 'solver/incompatibility_cause.dart';
 import 'source/cached.dart';
 import 'source/git.dart';
 import 'source/hosted.dart';