migrations: drop not null from documentation.html

Change-Id: I71906021838a5dad16497a78cc10768256b36425
Reviewed-on: https://go-review.googlesource.com/c/pkgsite/+/272788
Trust: Jonathan Amsterdam <jba@google.com>
Run-TryBot: Jonathan Amsterdam <jba@google.com>
Reviewed-by: Julie Qiu <julie@golang.org>
TryBot-Result: kokoro <noreply+kokoro@google.com>

migrations/000051_drop_documentation_html_not_null.down.sql

@@ -0,0 +1,10 @@
+-- Copyright 2020 The Go Authors. All rights reserved.
+-- Use of this source code is governed by a BSD-style
+-- license that can be found in the LICENSE file.
+
+BEGIN;
+
+ALTER TABLE documentation
+    ALTER COLUMN html SET NOT NULL;
+
+END;

migrations/000051_drop_documentation_html_not_null.up.sql

@@ -0,0 +1,10 @@
+-- Copyright 2020 The Go Authors. All rights reserved.
+-- Use of this source code is governed by a BSD-style
+-- license that can be found in the LICENSE file.
+
+BEGIN;
+
+ALTER TABLE documentation
+    ALTER COLUMN html DROP NOT NULL;
+
+END;