Fix scale type in JSON format

BUG=skia:
R=bensong@google.com, jcgregorio@google.com

Author: kelvinly@google.com

Review URL: https://codereview.chromium.org/354953007
diff --git a/bench/skpbench.json b/bench/skpbench.json
index b9a8fec..1e0e23f 100644
--- a/bench/skpbench.json
+++ b/bench/skpbench.json
@@ -86,7 +86,7 @@
                 },
                 {
                     "name": "scale",
-                    "type": "STRING"
+                    "type": "FLOAT"
                 },
                 {
                     "name": "bbh",