Fix shellcheck warnings

Author: edolstra

tests/functional/git-hashing/fixed.sh

@@ -1,3 +1,5 @@
+#!/usr/bin/env bash
+
 source common.sh
 
 # Store layer needs bugfix

tests/functional/help.sh

@@ -25,7 +25,7 @@ done
 
 # FIXME: we don't know whether we built the manpages, so we can't
 # reliably test them here.
-exit 0
+if false; then
 
 # test help output
 
@@ -74,3 +74,5 @@ nix-daemon --help
 nix-hash --help
 nix-instantiate --help
 nix-prefetch-url --help
+
+fi