Add JSHint rule to disallow invalid space characters

[dpilafian]

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Configure the project to enforce the JSHint rule that prohibits non-breaking whitespace characters.

See "jshintConfig" in package.json: https://github.com/center-key/pretty-print-json/blob/master/package.json#L21

JSHint documentation: https://jshint.com/docs/options/#nonbsp