docs: fix example return value

PR-URL: 	#2186
Reviewed-by: Athan Reines <[email protected]>
Signed-off-by: GUNJ JOSHI <[email protected]>

Author: gunjjoshi

lib/node_modules/@stdlib/math/base/special/rcbrt/docs/types/index.d.ts

@@ -42,7 +42,7 @@
 *
 * @example
 * var v = rcbrt( -8.0 );
-* // returns -2.0
+* // returns -0.5
 *
 * @example
 * var v = rcbrt( NaN );