Fix build by babel

.babelrc

@@ -1,5 +1,8 @@
 {
   "presets": [
-    "react-app"
+    "@babel/react"
+  ],
+  "plugins": [
+    "@babel/plugin-proposal-class-properties"
   ]
 }

package.json

@@ -50,8 +50,9 @@
   "devDependencies": {
     "@babel/cli": "^7.4.4",
     "@babel/core": "^7.4.5",
+    "@babel/plugin-proposal-class-properties": "^7.5.0",
+    "@babel/preset-react": "^7.0.0",
     "babel-polyfill": "^6.26.0",
-    "babel-preset-react-app": "^9.0.0",
     "codecov": "^3.5.0",
     "concurrently": "^4.1.0",
     "enzyme": "^3.10.0",

yarn.lock

@@ -141,6 +141,18 @@
     "@babel/helper-replace-supers" "^7.4.4"
     "@babel/helper-split-export-declaration" "^7.4.4"
 
+"@babel/helper-create-class-features-plugin@^7.5.0":
+  version "7.5.0"
+  resolved "https://registry.yarnpkg.com/@babel/helper-create-class-features-plugin/-/helper-create-class-features-plugin-7.5.0.tgz#02edb97f512d44ba23b3227f1bf2ed43454edac5"
+  integrity sha512-EAoMc3hE5vE5LNhMqDOwB1usHvmRjCDAnH8CD4PVkX9/Yr3W/tcz8xE8QvdZxfsFBDICwZnF2UTHIqslRpvxmA==
+  dependencies:
+    "@babel/helper-function-name" "^7.1.0"
+    "@babel/helper-member-expression-to-functions" "^7.0.0"
+    "@babel/helper-optimise-call-expression" "^7.0.0"
+    "@babel/helper-plugin-utils" "^7.0.0"
+    "@babel/helper-replace-supers" "^7.4.4"
+    "@babel/helper-split-export-declaration" "^7.4.4"
+
 "@babel/helper-define-map@^7.4.0", "@babel/helper-define-map@^7.4.4":
   version "7.4.4"
   resolved "https://registry.yarnpkg.com/@babel/helper-define-map/-/helper-define-map-7.4.4.tgz#6969d1f570b46bdc900d1eba8e5d59c48ba2c12a"
@@ -317,6 +329,14 @@
     "@babel/helper-create-class-features-plugin" "^7.4.0"
     "@babel/helper-plugin-utils" "^7.0.0"
 
+"@babel/plugin-proposal-class-properties@^7.5.0":
+  version "7.5.0"
+  resolved "https://registry.yarnpkg.com/@babel/plugin-proposal-class-properties/-/plugin-proposal-class-properties-7.5.0.tgz#5bc6a0537d286fcb4fd4e89975adbca334987007"
+  integrity sha512-9L/JfPCT+kShiiTTzcnBJ8cOwdKVmlC1RcCf9F0F9tERVrM4iWtWnXtjWCRqNm2la2BxO1MPArWNsU9zsSJWSQ==
+  dependencies:
+    "@babel/helper-create-class-features-plugin" "^7.5.0"
+    "@babel/helper-plugin-utils" "^7.0.0"
+
 "@babel/[email protected]":
   version "7.4.0"
   resolved "https://registry.yarnpkg.com/@babel/plugin-proposal-decorators/-/plugin-proposal-decorators-7.4.0.tgz#8e1bfd83efa54a5f662033afcc2b8e701f4bb3a9"