install m4 O_o

.github/workflows/main.yml

@@ -20,7 +20,7 @@ jobs:
           sudo add-apt-repository ppa:avsm/ppa -y # provides OPAM 2
           sudo add-apt-repository ppa:haxe/ocaml -y # provides newer version of mbedtls
           sudo apt-get update -qqy
-          sudo apt-get install -qqy ocaml-nox camlp5 opam libpcre3-dev zlib1g-dev libgtk2.0-dev libmbedtls-dev ninja-build neko neko-dev
+          sudo apt-get install -qqy ocaml-nox camlp5 opam libpcre3-dev zlib1g-dev libgtk2.0-dev libmbedtls-dev ninja-build neko neko-dev m4
 
       - name: Install OCaml libraries
         run: |