docs: set sign to double

lib/node_modules/@stdlib/math/base/special/riemann-zeta/src/main.c

@@ -548,25 +548,25 @@ static double rational_p6q6( const double x ) {
 * // returns ~1.202
 */
 static double series( const double s ) {
-	uint8_t sign;
+	double sign;
 	double term;
 	double sum;
 	double tmp;
 	int32_t N2;
 	int32_t i;
 
 	sum = 0.0;
-	sign = 1;
+	sign = 1.0;
 	for ( i = 0; i < N; i++ ) {
 		sum += sign * NEG_TWO_N / stdlib_base_pow( (double)( i + 1 ), s );
-		sign *= -1; // flip the sign
+		sign *= -1.0; // flip the sign
 	}
 	tmp = 1.0;
 	term = 1.0;
 	N2 = 2 * N;
 	for ( i = N; i <= N2 - 1; i++ ) {
 		sum += sign * ( tmp - TWO_N ) / stdlib_base_pow( (double)( i + 1 ), s );
-		sign *= -1; // flip the sign
+		sign *= -1.0; // flip the sign
 		term *= N2 - i;
 		term /= i - N + 1.0;
 		tmp += term;