Upgrade dependencies, remove unused dependency (MetaMask#165)

- `yarn upgrade --latest --caret`
- Remove unused plugins: `@vuepress/plugin-google-analytics`, `vuepress-plugin-flowchart`
- Move all dependencies to `devDependencies`

package.json

@@ -26,19 +26,16 @@
   },
   "homepage": "https://github.com/MetaMask/metamask-docs",
   "devDependencies": {
-    "@vuepress/plugin-back-to-top": "^1.0.3",
-    "@vuepress/plugin-google-analytics": "^1.0.3",
-    "@vuepress/plugin-medium-zoom": "^1.0.3",
-    "@vuepress/plugin-pwa": "^1.0.3",
-    "@vuepress/theme-vue": "^1.0.3",
-    "prettier": "^2.0.5",
-    "vue-toasted": "^1.1.25",
-    "vuepress": "^1.0.3",
-    "vuepress-plugin-flowchart": "^1.4.2",
-    "vuepress-plugin-redirect": "^1.2.3"
-  },
-  "dependencies": {
+    "@vuepress/plugin-back-to-top": "^1.5.4",
+    "@vuepress/plugin-medium-zoom": "^1.5.4",
+    "@vuepress/plugin-pwa": "^1.5.4",
+    "@vuepress/theme-vue": "^1.5.4",
+    "prettier": "^2.1.1",
     "vue-tabs-component": "^1.5.0",
+    "vue-toasted": "^1.1.28",
+    "vuepress": "^1.5.4",
+    "vuepress-plugin-redirect": "^1.2.4",
     "vuepress-plugin-tabs": "^0.3.0"
-  }
+  },
+  "dependencies": {}
 }