I had the same problem, but I was able to get it working by running npm install --save-dev @babel/plugin-proposal-decorators and adding ["@babel/plugin-proposal-decorators", { "legacy": true }] to the plugins section in my .babelrc.
The plugins section of .babelrc, for me, now looks like this:
"plugins": [
["@babel/plugin-proposal-decorators", { "legacy": true }]
]