Upgrade metrics-sharelatex to 2.6.2

This version fixes the HTTP request timing metrics, which were not
reporting correctly.

services/track-changes/package.json

@@ -28,7 +28,7 @@
     "heap": "^0.2.6",
     "line-reader": "^0.4.0",
     "logger-sharelatex": "^1.9.0",
-    "metrics-sharelatex": "^2.6.1",
+    "metrics-sharelatex": "^2.6.2",
     "mongo-uri": "^0.1.2",
     "mongojs": "3.1.0",
     "redis": "~0.10.1",