get the right date string replacement for candlestick mock

Author: alexcjohnson

test/image/mocks/candlestick_double-y-axis.json

@@ -1947,8 +1947,8 @@
   "layout": {
     "xaxis": {
       "range": [
-        "2016-01-10 14:24:21.917",
-        "2016-08-15 01:54:22.978"
+        "2016-01-10 19:24:21.917",
+        "2016-08-15 05:54:22.978"
       ]
     },
     "yaxis": {