Upgrade electron to 1.6.8 (#1848)

* Upgrade deps

* Remove --harmony flag

* Add --harmony-async-await flag

* Pin deps

* Use cheap-module-source-map for dev

See https://github.com/webpack/webpack/issues/2145#issuecomment-294361203

* Update yarn.lock

package.json

@@ -50,7 +50,13 @@
           "minify-flip-comparisons",
           "minify-guarded-expressions",
           "minify-infinity",
-          ["minify-mangle-names", { "keepClassName": true, "keepFnName": true }],
+          [
+            "minify-mangle-names",
+            {
+              "keepClassName": true,
+              "keepFnName": true
+            }
+          ],
           "minify-replace",
           "minify-simplify",
           "minify-type-constructors",
@@ -117,18 +123,18 @@
   },
   "devDependencies": {
     "ava": "0.17.0",
-    "babel-cli": "6.18.0",
-    "babel-core": "6.18.0",
+    "babel-cli": "6.24.1",
+    "babel-core": "6.24.1",
     "babel-loader": "6.2.10",
-    "babel-preset-babili": "0.0.9",
-    "babel-preset-react": "6.16.0",
+    "babel-preset-babili": "0.0.12",
+    "babel-preset-react": "6.24.1",
     "copy-webpack-plugin": "4.0.0",
     "cross-env": "3.1.3",
-    "electron": "1.4.16",
+    "electron": "1.6.8",
     "electron-builder": "13.6.0",
+    "electron-builder-squirrel-windows": "13.6.1",
     "electron-devtools-installer": "2.0.0",
     "electron-rebuild": "1.5.10",
-    "electron-builder-squirrel-windows": "13.6.1",
     "eslint-config-xo-react": "0.10.0",
     "eslint-plugin-react": "6.7.1",
     "husky": "0.11.6",