Attempt to fix failures on the windows bot

Change-Id: I5fcda7cc11979dcde7948ffa4cfa53a5ee4e07e2
Reviewed-on: https://dart-review.googlesource.com/68162
Commit-Queue: Brian Wilkerson <brianwilkerson@google.com>
Reviewed-by: Konstantin Shcheglov <scheglov@google.com>

Author: bwilkerson

pkg/analysis_server/test/domain_completion_test.dart

@@ -649,7 +649,7 @@ main() {
   test_local_override() {
     newFile('/libA.dart', content: 'class A {m() {}}');
     addTestFile('''
-import '/libA.dart';
+import '../../libA.dart';
 class B extends A {
   m() {}
   x() {^}
@@ -720,7 +720,7 @@ main() {
   test_overrides() {
     newFile('/libA.dart', content: 'class A {m() {}}');
     addTestFile('''
-import '/libA.dart';
+import '../../libA.dart';
 class B extends A {m() {^}}
 ''');
     return getSuggestions().then((_) {