intro: change byline to "by al." (#6984)

Several people have suggested that the "by Bram" byline is misleading,
it implies that Bram is actively involved with the project. Up to now we
left it as an homage.

Bram agreed that it is misleading, and suggested a mention somewhere
other than the intro.

src/nvim/version.c

@@ -993,7 +993,7 @@ void intro_message(int colon)
   static char *(lines[]) = {
     N_(NVIM_VERSION_LONG),
     "",
-    N_("by Bram Moolenaar et al."),
+    N_("by al."),
     N_("Nvim is open source and freely distributable"),
     N_("https://neovim.io/community"),
     "",