Updated linting

Author: leoafarias

lib/src/models/latest_version_model.dart

@@ -29,5 +29,5 @@ class LatestVersion {
 
   @override
   String toString() =>
-      'LatestVersion(needUpdate: $needUpdate, latestVersion: $latestVersion, packageInfo: $packageInfo)';
+      '''LatestVersion(needUpdate: $needUpdate, latestVersion: $latestVersion, packageInfo: $packageInfo)''';
 }

lib/src/models/package_documentation_model.dart

@@ -98,5 +98,5 @@ class PackageDocumentationVersion {
 
   @override
   String toString() =>
-      'PackageDocumentationVersion(version: $version, status: $status, hasDocumentation: $hasDocumentation)';
+      '''PackageDocumentationVersion(version: $version, status: $status, hasDocumentation: $hasDocumentation)''';
 }

lib/src/models/package_options_model.dart

@@ -25,7 +25,7 @@ class PackageOptions {
 
   @override
   String toString() =>
-      'PackageOptions(isDiscontinued: $isDiscontinued, isUnlisted: $isUnlisted, replacedBy: $replacedBy)';
+      '''PackageOptions(isDiscontinued: $isDiscontinued, isUnlisted: $isUnlisted, replacedBy: $replacedBy)''';
 
   @override
   bool operator ==(Object other) {

lib/src/models/pub_package_model.dart

@@ -87,7 +87,7 @@ class PackageVersion {
 
   @override
   String toString() =>
-      'PackageVersion(version: $version, pubspec: $pubspec, archiveUrl: $archiveUrl, published: $published)';
+      '''PackageVersion(version: $version, pubspec: $pubspec, archiveUrl: $archiveUrl, published: $published)''';
 
   @override
   bool operator ==(Object other) {