Invalid json is returned when Git LFS requests return error messages

Issue Summary

In cases where Git LFS requests lead to an error, the message contains "\n" characters, which are invalid in the json response (and can cause the client not to show the message)
 

Steps to Reproduce

For an authentication error, as an example, the server returns the following json response:

{"message":"Not authenticated

Please authenticate and try your request again."}

Note that after "Not authenticated" the message contains two "\n" characters.

The git lfs command-line client is unable to parse the message, and instead shows the following:

batch response: Authentication required: Unable to parse HTTP response for POST <URL>: invalid character '\n' in string literal

Workaround

A workaround, to see the actual error message, is to enable git debug logging (eg GIT_TRACE=1)