Cannot convert a Symbol value to a string

[jasonkarns]

When attempting to console log an object that has stubbed methods:

message: Cannot convert a Symbol value to a string
  stacktrace: TypeError: Cannot convert a Symbol value to a string
    at Object.get (/Users/jasonkarns/Projects/shutterstock/little-sister/node_modules/testdouble/lib/object.js:61:67)
    at formatValue (util.js:420:38)
    at formatProperty (util.js:828:11)
    at formatObject (util.js:644:17)
    at formatValue (util.js:606:18)
    at inspect (util.js:321:10)
    at format (util.js:188:12)
    at Console.log (console.js:127:21)
    at LittleSister.parseEventValue (/Users/jasonkarns/Projects/shutterstock/little-sister/src/index.js:84:11)
    at propsFromDataTrack (/Users/jasonkarns/Projects/shutterstock/little-sister/src/index.js:78:17)

I believe this is related to (or a dupe of #124)

Investigation:

The error traces to: https://github.com/testdouble/testdouble.js/blob/v3.2.6/src/object.js#L38
which compiles as: https://github.com/testdouble/testdouble.js/blob/v3.2.6/dist/testdouble.js#L10675

According to nodejs/node#927 (comment), implicit string conversion is not allowed on symbols.