change migration order

apps/explorer/priv/repo/migrations/20191121064805_add_block_hash_and_block_index_to_logs.exs

@@ -7,8 +7,6 @@ defmodule Explorer.Repo.Migrations.AddBlockHashAndBlockIndexToLogs do
       add(:block_number, :integer)
     end
 
-    create(index(:logs, [:block_number]))
-
     execute("""
     UPDATE logs log
     SET block_hash = with_block.block_hash,
@@ -25,6 +23,8 @@ defmodule Explorer.Repo.Migrations.AddBlockHashAndBlockIndexToLogs do
     ;
     """)
 
+    create(index(:logs, [:block_number]))
+
     alter table(:logs) do
       modify(:block_hash, references(:blocks, column: :hash, type: :bytea), null: false)
     end