Update docs to include transformHeader config

docs/docs.html

@@ -341,6 +341,7 @@ var csv = Papa.unparse({
 	escapeChar: '"',
 	header: false,
 	trimHeaders: false,
+	transformHeader: undefined,
 	dynamicTyping: false,
 	preview: 0,
 	encoding: "",
@@ -418,6 +419,14 @@ var csv = Papa.unparse({
 									If true leading/trailing spaces will be trimed from headers.
 								</td>
 							</tr>
+							<tr>
+								<td>
+									<code>transformHeader</code>
+								</td>
+								<td>
+									A function to apply on each header. Requires <code>header</code> to be <code>true</code>. The function receives the header as its first argument. The <code>transformHeader</code> function is applied after <code>trimHeaders</code> if enabled.
+								</td>
+							</tr>
 							<tr>
 								<td>
 									<code>dynamicTyping</code>