perf: Make learn-ocaml build parallel by default

(now that it's fixed)

Author: AltGr

src/main/learnocaml_main.ml

@@ -194,7 +194,7 @@ module Args = struct
          the entire repository. Can be repeated."
 
     let jobs =
-      value & opt int 1 & info ["jobs";"j"] ~docv:"INT" ~doc:
+      value & opt int 8 & info ["jobs";"j"] ~docv:"INT" ~doc:
         "Number of building jobs to run in parallel"
 
     type t = {