Fix buffer trim while sending websocket messages

[mojojoji]

Buffer.from creates a new buffer of the same length of initial buffer or data. The data send over websocket needs to append one byte to identify message type (stdout/stdin/sterr).
This merge request creates the buffer with length = 1+ data length and copies over the data/

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[mojojoji]

/assign @brendandburns

[itowlson]

@mojojoji Looks like the CLA is not coming through which is blocking the merge... could you check the status and that the email addresses tally please? (Or post another comment and see if that makes it take notice!) Thanks!

[mojojoji]

CLA signed

[mojojoji]

fixes #112

[brendandburns]

/lgtm
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: brendandburns, mojojoji

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