fix compilation errors

.babelrc

@@ -1,10 +1,5 @@
 {
-  "presets": [
+  "presets": ["@babel/preset-typescript", ["@babel/env"]],
-    "@babel/preset-typescript",
-    ["@babel/env"]
-  ],
   "compact": true,
-  "plugins": [
+  "plugins": ["lodash", "@babel/plugin-proposal-class-properties"]
-    "lodash"
-  ]
 }

package.json

@@ -77,6 +77,7 @@
   "devDependencies": {
     "@babel/core": "^7.5.5",
     "@babel/node": "^7.5.5",
+    "@babel/plugin-proposal-class-properties": "^7.7.4",
     "@babel/preset-env": "^7.5.5",
     "@babel/preset-typescript": "^7.3.3",
     "@babel/register": "^7.5.5",

webpack.config.babel.js

@@ -94,7 +94,7 @@ export default [
                   },
                 ],
               ],
-              plugins: ['lodash'],
+              plugins: ['lodash', '@babel/plugin-proposal-class-properties'],
             },
           },
         },

yarn.lock

@@ -259,6 +259,14 @@
     "@babel/helper-remap-async-to-generator" "^7.7.4"
     "@babel/plugin-syntax-async-generators" "^7.7.4"
 
+"@babel/plugin-proposal-class-properties@^7.7.4":
+  version "7.7.4"
+  resolved "https://registry.yarnpkg.com/@babel/plugin-proposal-class-properties/-/plugin-proposal-class-properties-7.7.4.tgz#2f964f0cb18b948450362742e33e15211e77c2ba"
+  integrity sha512-EcuXeV4Hv1X3+Q1TsuOmyyxeTRiSqurGJ26+I/FW1WbymmRRapVORm6x1Zl3iDIHyRxEs+VXWp6qnlcfcJSbbw==
+  dependencies:
+    "@babel/helper-create-class-features-plugin" "^7.7.4"
+    "@babel/helper-plugin-utils" "^7.0.0"
+
 "@babel/plugin-proposal-dynamic-import@^7.7.4":
   version "7.7.4"
   resolved "https://registry.yarnpkg.com/@babel/plugin-proposal-dynamic-import/-/plugin-proposal-dynamic-import-7.7.4.tgz#dde64a7f127691758cbfed6cf70de0fa5879d52d"