Switch to xxhash to save farmhash jiggery-pokery when initialising Docker image

package.json

@@ -27,7 +27,6 @@
     "buffers": "NuSkooler/node-buffers",
     "bunyan": "^1.8.12",
     "exiftool": "^0.0.3",
-    "farmhash": "^2.0.4",
     "fs-extra": "^4.0.1",
     "graceful-fs": "^4.1.11",
     "hashids": "^1.1.1",
@@ -52,6 +51,7 @@
     "uuid": "^3.1.0",
     "uuid-parse": "^1.0.0",
     "ws": "^3.1.0",
+    "xxhash": "^0.2.4",
     "yazl" : "^2.4.2"
   },
   "devDependencies": {},