[test] fix Sixspeed runner to really run "Map get string"

Bug: 
Change-Id: I4ffc052bb9f4599c91f0ad6a5ed41ac622c911d1
Reviewed-on: https://chromium-review.googlesource.com/735439Reviewed-by: Peter Marshall <petermarshall@chromium.org>
Commit-Queue: Tobias Tebbi <tebbi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48878}

test/js-perf-test/SixSpeed.json

@@ -258,14 +258,14 @@
         {
           "name": "ES5",
           "main": "run.js",
-          "resources": ["map_set_add/es5.js"],
-          "test_flags": ["map_set_add/es5"]
+          "resources": ["map_string/es5.js"],
+          "test_flags": ["map_string/es5"]
         },
         {
           "name": "ES6",
           "main": "run.js",
-          "resources": ["map_set_add/es6.js"],
-          "test_flags": ["map_set_add/es6"]
+          "resources": ["map_string/es6.js"],
+          "test_flags": ["map_string/es6"]
         }
       ]
     }