Fix pub_test.

I forgot to update the --help output here.

R=rnystrom@google.com

Review URL: https://codereview.chromium.org//1220543006.

test/pub_test.dart

@@ -17,17 +17,19 @@ main() {
         Usage: pub <command> [arguments]
 
         Global options:
-        -h, --help            Print this usage information.
-            --version         Print pub version.
-            --[no-]trace      Print debugging information when an error occurs.
-            --verbosity       Control output verbosity.
-
-                  [all]       Show all output including internal tracing messages.
-                  [io]        Also show IO operations.
-                  [normal]    Show errors, warnings, and user messages.
-                  [solver]    Show steps during version resolution.
-
-        -v, --verbose         Shortcut for "--verbosity=all".
+        -h, --help                     Print this usage information.
+            --version                  Print pub version.
+            --[no-]trace               Print debugging information when an error occurs.
+            --verbosity                Control output verbosity.
+
+                  [all]                Show all output including internal tracing messages.
+                  [io]                 Also show IO operations.
+                  [normal]             Show errors, warnings, and user messages.
+                  [solver]             Show steps during version resolution.
+
+        -v, --verbose                  Shortcut for "--verbosity=all".
+            --[no-]package-symlinks    Generate packages/ directories when installing packages.
+                                       (defaults to on)
 
         Available commands:
           build       Apply transformers to build a package.