fix proposals table unable to rollback

database/migrations/2018_07_08_194000_create_proposals_table.php

@@ -53,6 +53,11 @@ class CreateProposalsTable extends Migration
      */
     public function down()
     {
+        // remove the FK
+        Schema::table('revisions', function (Blueprint $table) {
+            $table->dropForeign('revisions_proposal_id_foreign');
+        });
+
         Schema::dropIfExists('proposals');
     }
 }