devserver: Minor fix to option help string.

Makes it clear that starting with --port=0 will always work.

BUG=chromium:322436
TEST=None

Change-Id: I68e2d4d34a3eb3c98e96c2898b3e0e11354f40ad
Reviewed-on: https://chromium-review.googlesource.com/186696
Tested-by: Gilad Arnold <garnold@chromium.org>
Reviewed-by: Don Garrett <dgarrett@chromium.org>
Commit-Queue: Gilad Arnold <garnold@chromium.org>
diff --git a/devserver.py b/devserver.py
index 1b09ef2..73fb39a 100755
--- a/devserver.py
+++ b/devserver.py
@@ -1059,9 +1059,8 @@
                     help='writable static directory')
   parser.add_option('--port',
                     default=8080, type='int',
-                    help=('port for the dev server to use; if zero, then we '
-                          'attempt to allocate an available port '
-                          '(default: 8080)'))
+                    help=('port for the dev server to use; if zero, binds to '
+                          'an arbitrary available port (default: 8080)'))
   parser.add_option('-t', '--test_image',
                     action='store_true',
                     help='Deprecated.')