nvim: only load gentoo-syntax for ebuilds

.config/nvim/lua/coding.lua

@@ -33,5 +33,6 @@ packer.use {
     config = function()
         -- vim.g.syntastic_ebuild_checkers = { 'pkgcheck' }
         vim.g.syntastic_sh_checkers = { 'sh', 'checkbashisms' }
-    end
+    end,
+    ft = 'ebuild'
 }