Add postcss-loader && update echarts

package.json

@@ -17,7 +17,7 @@
     "clipboard": "1.7.1",
     "codemirror": "5.31.0",
     "dropzone": "5.2.0",
-    "echarts": "3.7.2",
+    "echarts": "3.8.2",
     "element-ui": "2.0.2",
     "file-saver": "1.3.3",
     "font-awesome": "4.7.0",
@@ -73,6 +73,7 @@
     "opn": "4.0.2",
     "optimize-css-assets-webpack-plugin": "3.2.0",
     "ora": "1.1.0",
+    "postcss-loader": "^2.0.8",
     "pushstate-server": "2.1.0",
     "rimraf": "2.6.0",
     "sass-loader": "6.0.6",