Fix a typo with astro.h

Bug:chromium:726654
Test: gn gen works without an error
Review-Url: https://codereview.chromium.org/2913423002 .
diff --git a/BUILD.gn b/BUILD.gn
index 4d585c9..20ade24 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -450,7 +450,7 @@
   ]
   # ls source/i18n/unicode/*h | sort | sed 's/^\(.*\)$/    "\1",/'
   public = [
-    // crbug.com/726654: Make astro.h public until the upstream adds an API.
+    # crbug.com/726654: Make astro.h public until the upstream adds an API.
     "source/i18n/astro.h",
     "source/i18n/unicode/alphaindex.h",
     "source/i18n/unicode/basictz.h",