tiny fix for warning

src/camel/exec/writeChi2.cc

@@ -38,7 +38,7 @@ int main(int argc,char** argv){
   }
   cout << "Some derived parameters:" << endl;
   //print a number of cosmological values
-  char* extra[]={"H0","z_reio","tau_reio","z_drag","rs_drag","Dv(0.57)","Da(0.57)","H(0.57)", "f(0.57)"};
+  const char* extra[]={"H0","z_reio","tau_reio","z_drag","rs_drag","Dv(0.57)","Da(0.57)","H(0.57)", "f(0.57)"};
   const int N=sizeof(extra)/sizeof(char*);
   for (size_t i=0;i<N;i++) {
     double val(0.);