bump electron-snapshot version

package.json

@@ -60,7 +60,7 @@
     "cson-parser": "^1.3.3",
     "debounce": "^1.0.0",
     "documentdb": "^1.5.1",
-    "electron-mksnapshot": "1.6.0",
+    "electron-mksnapshot": "1.7.1",
     "eslint": "^3.4.0",
     "event-stream": "^3.1.7",
     "express": "^4.13.1",