gmsh: 3.0.5 -> 3.0.6

Semi-automatic update. These checks were done:

- built on NixOS
- Warning: no binary found that responded to help or version flags. (This warning appears even if the package isn't expected to have binaries.)
- found 3.0.6 with grep in /nix/store/ha4gl4kswiq7pz4chb1ba9ixb51rcdsn-gmsh-3.0.6
- found 3.0.6 in filename of file in /nix/store/ha4gl4kswiq7pz4chb1ba9ixb51rcdsn-gmsh-3.0.6