SystemHealthSmokeTest: Fixed disable message typo.

Bug: 726439
Change-Id: Ia688e6b35c33e48353d371476991c35559eb1b7d
Reviewed-on: https://chromium-review.googlesource.com/516865Reviewed-by: Ned Nguyen <nednguyen@google.com>
Commit-Queue: Matt Giuca <mgiuca@chromium.org>
Cr-Commit-Position: refs/heads/master@{#475776}

tools/perf/benchmarks/system_health_smoke_test.py

@@ -98,7 +98,7 @@ def _GenerateSmokeTestCase(benchmark_class, story_to_smoke_test):
       self.skipTest('Benchmark %s is disabled' % SinglePageBenchmark.Name())
 
     if self.id() in _DISABLED_TESTS:
-      self.skipTest('Test is explictly disabled')
+      self.skipTest('Test is explicitly disabled')
 
     self.assertEqual(0, SinglePageBenchmark().Run(options),
                      msg='Failed: %s' % benchmark_class)