electron-mail: use `--replace-fail`

Signed-off-by: Ludovico Piero <[e-mail]>

pkgs/by-name/el/electron-mail/package.nix

···
   extraInstallCommands = ''
     install -m 444 -D ${appimageContents}/${pname}.desktop -t $out/share/applications
     substituteInPlace $out/share/applications/${pname}.desktop \
-      --replace 'Exec=AppRun' 'Exec=${pname}'
+      --replace-fail 'Exec=AppRun' 'Exec=${pname}'
     cp -r ${appimageContents}/usr/share/icons $out/share
   '';