Swap getUsage() for get usage in args package

pkg/args/lib/src/arg_parser.dart

Index: pkg/args/lib/src/arg_parser.dart
diff --git a/pkg/args/lib/src/arg_parser.dart b/pkg/args/lib/src/arg_parser.dart
index b1ee6280200885e982941823e3fa57b9aaa40659..03d8d3f55165197e7b297c6a070b5aced2a04655 100644
--- a/pkg/args/lib/src/arg_parser.dart
+++ b/pkg/args/lib/src/arg_parser.dart
@@ -115,8 +115,14 @@ class ArgParser {
   /// Generates a string displaying usage information for the defined options.
   ///
   /// This is basically the help text shown on the command line.
+  @Deprecated("Replaced with get usage. getUsage() will be removed in args 1.0")
   String getUsage() => new Usage(this).generate();
 
+  /// Generates a string displaying usage information for the defined options.
+  ///
+  /// This is basically the help text shown on the command line.
+  String get usage => new Usage(this).generate();
+
   /// Get the default value for an option. Useful after parsing to test if the
   /// user specified something other than the default.
   getDefault(String option) {