indicate lack of RESTRICT foreign key support in mssql dialect

MSSQL doesn't support RESTRICT foreign key constraints at all,
so there's no use running any of those tests

lib/dialects/mssql/index.js

@@ -15,6 +15,9 @@ MssqlDialect.prototype.supports = _.merge(_.cloneDeep(Abstract.prototype.support
   'RETURNING': true,
   'RETURNING': true,
   'LIMIT ON UPDATE': true,
   'LIMIT ON UPDATE': true,
   lock: false,
   lock: false,
+  constraints: {
+    restrict: false
+  },
   index: {
   index: {
     collate: false,
     collate: false,
     length: false,
     length: false,