Fix compilation on Windows

MSVC was (correctly) complaining that std::pow does not evaluate to a
constant -- this was added in C++20 (I believe), while we compile
assuming C++11.

Signed-off-by: Rodrigo Tobar <rtobar@icrar.org>

include/numerical_constants.h

@@ -95,7 +95,7 @@ namespace constants {
 	constexpr double MPC2CM = MPC2M * HECTO;
 
 	/** Number of centimetres in a Mpc (Particle Data Book 2002, page 6) cubed*/
-	constexpr double MPC2CM_cube = std::pow(MPC2CM, 3);
+	constexpr double MPC2CM_cube = pow<3>(MPC2CM);
 
 	/** Number of cm in a km */
 	constexpr double KM2CM = 1e5;