writers/write-bash-bin: add shellcheck pass

There's no checkPhase in the trivial builder, doing the check part of
the build itself.

This is fine :P

modules/lib/writers.scm

@@ -1,5 +1,6 @@
 (define-module (lib writers)
   #:use-module (gnu)
+  #:use-module (gnu packages haskell-apps)
   #:use-module (guix packages)
   #:use-module (guix build-system trivial)
   #:use-module (guix gexp)
@@ -25,7 +26,7 @@
              (mkdir-p (string-append #$output "/bin"))
              (copy-file #$(local-file script) bin-name)
              (chmod bin-name #o0555)
-             #t))))
+             (invoke #$(file-append shellcheck "/bin/shellcheck") bin-name)))))
     (home-page #f)
     (synopsis #f)
     (description #f)