Upgrade appimage runtime to fix armv6l support

https://github.com/AppImage/type2-runtime/issues/112

nix/appimagetool/default.nix

@@ -12,7 +12,7 @@
   # github, which is really cool, except that it doesn't preserve any older
   # builds of the project. And it's pretty difficult to build it ourselves. So
   # fuck it, just embed the build artifacts directly in this project.
-  runtimeFileVersion = "81de3e1";
+  runtimeFileVersion = "f6c0b18";
   runtimeFile = "${./.}/runtime-${arch}-${runtimeFileVersion}";
 
 in writeScriptBin "appimagetool" ''