csv export doesn't specify a default file encoding

[jawalonoski]

Discussed in #1130

The property exporter.encoding should have a default value.

synthea/src/main/java/org/mitre/synthea/export/CSVExporter.java

Lines 147 to 150 in 794345f

	/**
	* Charset for specifying the character set of the output files.
	*/
	private Charset charset = Charset.forName(Config.get("exporter.encoding"));