fix unnecessary_this lint for latest SDK (dart-lang/pubspec_parse#26)

pkgs/pubspec_parse/lib/src/dependency.dart

diff --git a/pkgs/pubspec_parse/lib/src/dependency.dart b/pkgs/pubspec_parse/lib/src/dependency.dart
index 07d08b5..3839e54 100644
--- a/pkgs/pubspec_parse/lib/src/dependency.dart
+++ b/pkgs/pubspec_parse/lib/src/dependency.dart
@@ -199,7 +199,7 @@
   final HostedDetails hosted;
 
   HostedDependency({VersionConstraint version, this.hosted})
-      : this.version = version ?? VersionConstraint.any,
+      : version = version ?? VersionConstraint.any,
         super._();
 
   @override

pkgs/pubspec_parse/lib/src/pubspec.dart

diff --git a/pkgs/pubspec_parse/lib/src/pubspec.dart b/pkgs/pubspec_parse/lib/src/pubspec.dart
index a5cba62..59ee585 100644
--- a/pkgs/pubspec_parse/lib/src/pubspec.dart
+++ b/pkgs/pubspec_parse/lib/src/pubspec.dart
@@ -65,11 +65,11 @@
     Map<String, Dependency> dependencies,
     Map<String, Dependency> devDependencies,
     Map<String, Dependency> dependencyOverrides,
-  })  : this.authors = _normalizeAuthors(author, authors),
-        this.environment = environment ?? const {},
-        this.dependencies = dependencies ?? const {},
-        this.devDependencies = devDependencies ?? const {},
-        this.dependencyOverrides = dependencyOverrides ?? const {} {
+  })  : authors = _normalizeAuthors(author, authors),
+        environment = environment ?? const {},
+        dependencies = dependencies ?? const {},
+        devDependencies = devDependencies ?? const {},
+        dependencyOverrides = dependencyOverrides ?? const {} {
     if (name == null || name.isEmpty) {
       throw new ArgumentError.value(name, 'name', '"name" cannot be empty.');
     }