Update test to assume build_runner behavior from 0.8.5 (#46)

Author: kevmoo

example/pubspec.yaml

@@ -8,5 +8,5 @@ dependencies:
   angular: ^5.0.0-alpha+10
 
 dev_dependencies:
-  build_runner: ^0.8.2
+  build_runner: ^0.8.5
   build_web_compilers: ^0.3.6

webdev/test/e2e_test.dart

@@ -53,6 +53,14 @@ void main() {
         process.stdout,
         emitsThrough(
             '[WARNING] Skipped creation of the merged output directory.'));
+
+    await expectLater(
+        process.stderr,
+        emitsThrough(
+            '[SEVERE] Unable to create merged directory for ${d.sandbox}. '
+            'Choose a different directory or delete the contents of that '
+            'directory'));
+
     await expectLater(process.stderr,
         emitsThrough('Failed to create merged output directories.'));