migrations: fix typo in 000096 down

The down migration INDEX idx_symbol_history_sort_version is fixed to
correctly refer to idx_symbol_history_sort_version.

Change-Id: I1c4fff26223326bd9c3f958b9a23adbafffa4cc7
Reviewed-on: https://go-review.googlesource.com/c/pkgsite/+/318649
Trust: Julie Qiu <julie@golang.org>
Run-TryBot: Julie Qiu <julie@golang.org>
TryBot-Result: kokoro <noreply+kokoro@google.com>
Reviewed-by: Jonathan Amsterdam <jba@google.com>
diff --git a/migrations/000096_add_symbol_history_goos_goarch_idx.down.sql b/migrations/000096_add_symbol_history_goos_goarch_idx.down.sql
index 0e32f45..5ee0f22 100644
--- a/migrations/000096_add_symbol_history_goos_goarch_idx.down.sql
+++ b/migrations/000096_add_symbol_history_goos_goarch_idx.down.sql
@@ -4,7 +4,7 @@
 
 BEGIN;
 
-DROP INDEX idx_symbol_history_module_sort_version;
+DROP INDEX idx_symbol_history_sort_version;
 DROP INDEX idx_symbol_history_goos;
 DROP INDEX idx_symbol_history_goarch;