webpack fix

[umitbilgin]

[vladaman]

@umitbilgin Is this fix for the following error or is it unrelated?

"TypeError: Right-hand side of 'instanceof' is not callable",
    "    at str (/var/task/index.js:39122:51)",

I am getting the error after running webpack at this line:

isBigNumber = value != null && (value instanceof BigNumber || BigNumber.isBigNumber(value));