use https for invisible island link

README.md

@@ -1261,7 +1261,7 @@ _For a more comprehensive/advanced/better categorized/... list of Linux audio so
 - [![Open-Source Software][oss icon]](https://github.com/gnunn1/tilix) [Tilix](https://gnunn1.github.io/tilix-web/) - A tiling terminal emulator for Linux using GTK+ 3.
 - [![Open-Source Software][oss icon]](https://github.com/cosmos72/twin) [Twin](https://github.com/cosmos72/twin/) - Fast, lightweight text-mode window environment with mouse support. Enables multiple terminals in a single Linux console, terminal or X11 window. It can be detached (keeps running in background) and reattached to a different console, terminal or X11 server. Works on Linux, Mac OS X and BSD.
 - [![Open-Source Software][oss icon]](https://github.com/saulpw/visidata) [Visidata](http://visidata.org/) - A terminal spreadsheet multitool for discovering and arranging data.
-- [![Open-Source Software][oss icon]](http://invisible-island.net/xterm/) [Xterm](https://invisible-island.net/xterm/) - The Xterm program is a terminal emulator for the X Window System. It provides DEC VT102 and Tektronix 4014 compatible terminals for programs that can't use the window system directly.
+- [![Open-Source Software][oss icon]](https://invisible-island.net/xterm/) [Xterm](https://invisible-island.net/xterm/) - The Xterm program is a terminal emulator for the X Window System. It provides DEC VT102 and Tektronix 4014 compatible terminals for programs that can't use the window system directly.
 - [![Open-Source Software][oss icon]](https://invent.kde.org/utilities/yakuake) [Yakuake](https://apps.kde.org/yakuake/) - A Quake-style terminal emulator based on KDE Konsole technology.
 - [![Open-Source Software][oss icon]](https://github.com/zellij-org/zellij) [Zellij](https://zellij.dev/) - A terminal workspace and multiplexer. Letting you open several panes and tabs to run different programs, share a terminal session with others and more. Very user friendly and intuitive.