Upgrade package:lints to 2.0.0 (#3445)

diff --git a/lib/src/packages_file.dart b/lib/src/packages_file.dart
index 6833ae8..d5c7989 100644
--- a/lib/src/packages_file.dart
+++ b/lib/src/packages_file.dart
@@ -80,7 +80,7 @@
       packageLocation = baseLocation.resolve(packageValue);
       if (!packageLocation.path.endsWith('/')) {
         packageLocation =
-            packageLocation.replace(path: packageLocation.path + "/");
+            packageLocation.replace(path: "${packageLocation.path}/");
       }
     }
     if (result.containsKey(packageName)) {
@@ -162,7 +162,7 @@
       uri = _relativize(uri, baseUri);
     }
     if (!uri.path.endsWith('/')) {
-      uri = uri.replace(path: uri.path + '/');
+      uri = uri.replace(path: '${uri.path}/');
     }
     output.write(uri);
     output.writeln();
@@ -251,7 +251,7 @@
     }
     assert(badIndex < packageName.length);
     var badCharCode = packageName.codeUnitAt(badIndex);
-    var badChar = "U+" + badCharCode.toRadixString(16).padLeft(4, '0');
+    var badChar = "U+${badCharCode.toRadixString(16).padLeft(4, '0')}";
     if (badCharCode >= 0x20 && badCharCode <= 0x7e) {
       // Printable character.
       badChar = "'${packageName[badIndex]}' ($badChar)";