tree-wide: fix instance of "meta.maintainer" -> "meta.maintainers"

Encountered one of these when using check-meta, did a quick
search to find other instances.

pkgs/misc/vscode-extensions/cpptools/default.nix

@@ -120,9 +120,9 @@ vscode-utils.buildVscodeMarketplaceExtension {
 
     meta = with stdenv.lib; {
       license = licenses.unfree;
-      maintainer = [ maintainers.jraygauthier ];
+      maintainers = [ maintainers.jraygauthier ];
       # A 32 bit linux would also be possible with some effort (specific download of binaries + 
       # patching of the elf files with 32 bit interpreter).
       platforms = [ "x86_64-linux" ];
     };
-}
+}