Fix refractive index output format

src/sphere/sphere.cpp

@@ -317,7 +317,7 @@ void sphere(string config_file, string data_file, string output_path) {
 	    } else {
 	      fprintf(
 		      output,
-		      "  SIZE=%15.7lE, REFRACTIVE INDEX=(%15.7lE,%15.7lE)\n",
+		      "  SIZE=%15.7lE, REFRACTIVE INDEX=%15.7lE%15.7lE\n",
 		      c2->vsz[i170],
 		      c2->vkt[i170].real(),
 		      c2->vkt[i170].imag()