Fix support of UMD. See https://github.com/umdjs/umd/blob/master/returnExports.js
Fix support of UMD. See https://github.com/umdjs/umd/blob/master/returnExports.js

vinodbonala/estraverse,goatslacker/estraverse,ghost23/estraverse,drom/estraverse,mysticatea/estraverse,estools/estraverse,dkoleary88/estraverse