scripts: Remove hyphen in the command name shown by `--version'.

* guix/scripts/build.scm (%options): Remove hyphen from the name passed
  to `show-version-and-exit'.
* guix/scripts/download.scm (%options): Likewise.
* guix/scripts/gc.scm (%options): Likewise.
* guix/scripts/import.scm (%options): Likewise.
* guix/scripts/package.scm (%options): Likewise.

guix/scripts/build.scm

@@ -105,7 +105,7 @@ Build the given PACKAGE-OR-DERIVATION and return their output paths.\n"))
                   (exit 0)))
         (option '(#\V "version") #f #f
                 (lambda args
-                  (show-version-and-exit "guix-build")))
+                  (show-version-and-exit "guix build")))
 
         (option '(#\S "source") #f #f
                 (lambda (opt name arg result)

guix/scripts/download.scm

@@ -104,7 +104,7 @@ and the hash of its contents.\n"))
                   (exit 0)))
         (option '(#\V "version") #f #f
                 (lambda args
-                  (show-version-and-exit "guix-download")))))
+                  (show-version-and-exit "guix download")))))
 
 
 ;;;

guix/scripts/gc.scm

@@ -97,7 +97,7 @@ interpreted."
                   (exit 0)))
         (option '(#\V "version") #f #f
                 (lambda args
-                  (show-version-and-exit "guix-gc")))
+                  (show-version-and-exit "guix gc")))
 
         (option '(#\C "collect-garbage") #f #t
                 (lambda (opt name arg result)

guix/scripts/import.scm

@@ -85,7 +85,7 @@ Import and convert the Nix expression ATTRIBUTE of NIXPKGS.\n"))
                   (exit 0)))
         (option '(#\V "version") #f #f
                 (lambda args
-                  (show-version-and-exit "guix-import")))))
+                  (show-version-and-exit "guix import")))))
 
 
 ;;;

guix/scripts/package.scm

@@ -327,7 +327,7 @@ Install, remove, or upgrade PACKAGES in a single transaction.\n"))
                   (exit 0)))
         (option '(#\V "version") #f #f
                 (lambda args
-                  (show-version-and-exit "guix-package")))
+                  (show-version-and-exit "guix package")))
 
         (option '(#\i "install") #t #f
                 (lambda (opt name arg result)