Build: fix the ci by adding a missing dune file in the bin dir

bin/dune

+(executable
+ (name gnuplotRifMain)
+  (libraries unix str num lutils)
+)
+(install
+ (section bin)
+ (files (gnuplotRifMain.exe as gnuplot-rif))
+)

lib/dune

 (library
   (name lutils)
   (public_name lutils)
-  (libraries unix str num stdlib-shims)
+  (libraries unix str num)
   (wrapped false)
   (synopsis "A lib shared by Verimag/synchronous tools (lustre-v6, lutin, rdbg).")
 )