title: Create table in bigquery fails when the JSON key contains hyphen
body: <p>I have a <strong>JSON</strong> data from Firebase Backup.
  Data generated is such that every key is preceded by a hyphen.</p>
  
  <p>Sample data is as follows:</p>
  
  <pre><code>"-GuGCJDEprMKczAMDUj8":{"deviceId":"399a649c6cee6209","dow":"Thursday","downloadFlag":"N","event":"streamStart","halfHourFull":"18h1","liveFlag":"Y","localDate":"2009-01-01","localHalfHour":1,"minutesSinceMidnight":1080,"quarterHourFull":"18q1","stationName":"hit 105","streamListenMethod":"Headphones","timestampLocal":"2009-01-01T18:00:33.679+10:00","timestampUTC":"2009-01-01T08:00:33.679Z"}
  </code></pre>
  
  <p>When we are trying to load that data into Bigquery then we are encountered with the below mentioned error:</p>
  
  <blockquote>
    <p>Fields must contain only letters, numbers, and underscores, start with
    a letter or underscore, and be at most 128 characters long.</p>
  </blockquote>
  
  <p>Is this a bigquery limitation? 
  If yes, then what's the proposed solution here.</p>
  
  <p>Any help/suggestion is much appreciated.</p>