add another missing include

Author: fredrik-johansson

arb_hypgeom/gamma_taylor.c

@@ -9,6 +9,7 @@
     (at your option) any later version.  See <http://www.gnu.org/licenses/>.
 */
 
+#include "flint/double_extras.h"
 #include "arb_hypgeom.h"
 
 #define DEBUG 0