[ashell] Special chars aren't supported in test-buffer.js

[xiaoyu3x]

Issue description

Copy test-buffer.js into ashell, 'Error: Newline is not allowed in strings or regexps' is outputed when run it.

Test Code

test-buffer.js

Steps to reproduce

1.Flash ashell into 101 board, then open port screen /dev/ttyACM0 115200.
2.Copy test-buffer.js to ashell and run it.

Actual Result

Expected Result

test-buffer.js run normally and no error.

Test Build

Branch	Commit id	Target Device	Test Date	Result
master	ede4509	Arduino 101	Feb 7, 2018	Fail