Bazel: Fix lint warning flagged by buildifier

Buildifier warns about missing wildcard pattern in glob parameter:

BUILD:30: constant-glob: Glob pattern `gr-editor/codemirror-assets.html`
has no wildcard ('*'). Constant patterns can be error-prone, move the
file outside the glob.

Change-Id: I09ad2dcdc7f43db97f0bce8cf49f4faff67a14d9
diff --git a/BUILD b/BUILD
index df4207a..feed56a 100644
--- a/BUILD
+++ b/BUILD
@@ -27,7 +27,7 @@
 
 bundle_assets(
     name = "codemirror-assets",
-    srcs = glob(["gr-editor/codemirror-assets.html"]),
+    srcs = ["gr-editor/codemirror-assets.html"],
     app = "gr-editor/codemirror-assets.html",
     split = False,
     deps = ["//lib/js:codemirror-minified"],