octave.desktop.in: Change Octave's XDG top-level category to Education. Suppresses warning message during install of octave.desktop and conforms to XDG suggested hierarchy for Science & Math applications. * octave.desktop.in: Change Octave's XDG top-level category to Education.

[Desktop Entry]
Name=GNU Octave
Comment=Scientific Computing using GNU Octave
TryExec=%OCTAVE_PREFIX%/bin/octave
Exec=%OCTAVE_PREFIX%/bin/octave
Icon=%OCTAVE_IMAGEDIR%/octave-logo.svg
Terminal=true
Type=Application
Categories=Education;Science;Math;
StartupNotify=false