Get rid of a lot of () for getters.

lib/core/options.dart

Index: lib/core/options.dart
diff --git a/lib/core/options.dart b/lib/core/options.dart
index 678de2fbd7565ecf5ba69b309f583e81b91f1b2c..1be8c12f148c8da2bf7f6f9bc9e7efd66d159413 100644
--- a/lib/core/options.dart
+++ b/lib/core/options.dart
@@ -23,7 +23,7 @@ interface Options default RuntimeOptions {
    * If the execution environment does not support [arguments] an empty list
    * is returned.
    */
-  List<String> get arguments();
+  List<String> get arguments;
 
   /**
    * Returns the path of the executable used to run the script in this
@@ -32,7 +32,7 @@ interface Options default RuntimeOptions {
    * If the execution environment does not support [executable] an empty
    * string is returned.
    */
-  String get executable();
+  String get executable;
 
   /**
    * Returns the path of the script being run in this isolate.
@@ -40,5 +40,5 @@ interface Options default RuntimeOptions {
    * If the executable environment does not support [script] an empty
    * string is returned.
    */
-  String get script();
+  String get script;
 }