Migration: fix formatting in nullability_node.dart

Change-Id: If81aa896e9774001a0c3a2d1d661bc58c41b9cdd
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/204425
Reviewed-by: Samuel Rawlins <srawlins@google.com>
Commit-Queue: Paul Berry <paulberry@google.com>

pkg/nnbd_migration/lib/src/nullability_node.dart

@@ -340,8 +340,7 @@ class NullabilityGraph {
   /// nullability information from one node to another.
   PropagationResult propagate() {
     if (_debugBeforePropagation) debugDump();
-    var propagationState =
-        _PropagationState(always, never).result;
+    var propagationState = _PropagationState(always, never).result;
     if (_debugAfterPropagation) debugDump();
     return propagationState;
   }