Warnings in RBF module

[andrea-iob]

Since #434 the RBF module issues this warning:

#13 111.0 In file included from /opt/bitpit/src/RBF/rbf.cpp:34:
#13 111.0 /opt/bitpit/src/RBF/rbf.hpp: In copy constructor 'bitpit::RBFKernel::RBFKernel(const bitpit::RBFKernel&)':
#13 111.0 /opt/bitpit/src/RBF/rbf.hpp:109:22: warning: 'bitpit::RBFKernel::m_polyActiveBasis' will be initialized after [-Wreorder]
#13 111.0   109 |     std::vector<int> m_polyActiveBasis;             /**< Active terms of linear polynomial, 0 is constant, i+1 the i-th system coordinate */
#13 111.0       |                      ^~~~~~~~~~~~~~~~~
#13 111.0 /opt/bitpit/src/RBF/rbf.hpp:108:22: warning:   'bitpit::RBFKernel::LinearPolynomial bitpit::RBFKernel::m_polynomial' [-Wreorder]
#13 111.0   108 |     LinearPolynomial m_polynomial;                  /**< Linear polynomial object */
#13 111.0       |                      ^~~~~~~~~~~~
#13 111.0 /opt/bitpit/src/RBF/rbf.cpp:87:1: warning:   when initialized here [-Wreorder]
#13 111.0    87 | RBFKernel::RBFKernel(const RBFKernel & other)
#13 111.0       | ^~~~~~~~~