chore(package): update @babel/plugin-proposal-class-properties to version 7.3.4

Closes #6

Author: greenkeeper[bot]

package.json

@@ -24,7 +24,7 @@
   },
   "devDependencies": {
     "@babel/core": "7.3.4",
-    "@babel/plugin-proposal-class-properties": "7.1.0",
+    "@babel/plugin-proposal-class-properties": "7.3.4",
     "@babel/plugin-proposal-decorators": "7.1.2",
     "@babel/plugin-proposal-export-namespace-from": "7.0.0",
     "@babel/plugin-syntax-dynamic-import": "7.0.0",