fix: made the required changes that were asked.

1. fixed the space before the outer paranthesis
2. corrected the title of the test cases which handles NaN inputs.

Author: nirmaljb

lib/node_modules/@stdlib/stats/incr/nanmmape/lib/main.js

@@ -73,7 +73,7 @@ function incrnanmmape( W ) {
 	* @returns {(number|null)} mean absolute percentage error or null
 	*/
 	function accumulator( f, a ) {
-		if ( arguments.length === 0 || isnan( f ) || isnan( a )) {
+		if ( arguments.length === 0 || isnan( f ) || isnan( a ) ) {
 			return mmape();
 		}
 		return mmape( f, a );

lib/node_modules/@stdlib/stats/incr/nanmmape/test/test.js

@@ -138,7 +138,7 @@ tape( 'if data has yet to be provided, the accumulator function returns `null`',
 	t.end();
 });
 
-tape( 'if provided `NaN`, the accumulated value is `NaN` for at least `W` invocations', function test( t ) {
+tape( 'if provided `NaN`, the accumulated function ignore it (returns the current mean absolute percentage error)', function test( t ) {
 	var expected;
 	var data;
 	var acc;