... operator for json will throw an exception

`var x={...{xx:1}}`

Error: Line 10: Unexpected token ...
at ErrorHandler.constructError (F:\theajack\tcon\node_modules\esprima\dist\esprima.js:5012:22)
at ErrorHandler.createError (F:\theajack\tcon\node_modules\esprima\dist\esprima.js:5028:27)
at Parser.unexpectedTokenError (F:\theajack\tcon\node_modules\esprima\dist\esprima.js:1985:39)

Reproduce the reported `var x={...{xx:1}}` input and trace the failure through the `node_modules/esprima/dist/esprima.js` stack locations shown in the report. Identify the parser entry point used by recast and add a regression test for object spread syntax; done means the input parses without the reported unexpected-token exception.

Written by the indexing model from the issue text.