Fix #2

This fixes #2 by tweaking `scripts/head.hackage` in two ways:

1. This changes the script to use
   `cabal new-update head.hackage.ghc.haskell.org`, not
   `cabal new-update head.hackage`, since the former is now the name
   of the `repository`. Since `head.hackage.ghc.haskell.org` is
   referred to in quite a few places in the script, I factored this
   out into its own variable.
2. This changes the `url` to use `http://`, not `https://`, so that
   `http-transport: plain-http` works properly. An alternative would
   be to keep the use of `https://` and use `http-transport: curl`
   instead, but that assumes the existence of a `curl` binary on
   one's machine, making it a less portable solution. In any case,
   the use of `http://` in this script shouldn't pose any security
   issues, since `hackage-security` already introduces a security
   layer independent of CAs.

scripts/head.hackage.sh

@@ -5,10 +5,12 @@ die () {
   exit 1
 }
 
+REPO=head.hackage.ghc.haskell.org
+
 cat_repo () {
 cat <<EOF
-repository head.hackage.ghc.haskell.org
-   url: https://ghc.gitlab.haskell.org/head.hackage/
+repository $REPO
+   url: http://ghc.gitlab.haskell.org/head.hackage/
    secure: True
    root-keys: 7541f32a4ccca4f97aea3b22f5e593ba2c0267546016b992dfadcd2fe944e55d
               26021a13b401500c8eb2761ca95c61f2d625bfef951b939a8124ed12ecf07329
@@ -57,18 +59,18 @@ case "X$1" in
     check_pkgcache
 
     if "$CABAL" new-update --help > /dev/null 2>&1; then
-      echo "INFO: '$CABAL' is recent enough and supports 'cabal new-update head.hackage'; you can try using that directly!"
+      echo "INFO: '$CABAL' is recent enough and supports 'cabal new-update $REPO'; you can try using that directly!"
       echo ""
 
       CFGFILE=$(mktemp)
       cat_repo > "$CFGFILE"
 
       # we need to wipe the cache for head.hackage to workaround issues in hackage-security
-      rm -rf "$PKGCACHE/head.hackage/"
+      rm -rf "$PKGCACHE/$REPO/"
 
       echo "http-transport: plain-http" >> "$CFGFILE"
 
-      "$CABAL" --project-file="$CFGFILE" new-update head.hackage
+      "$CABAL" --project-file="$CFGFILE" new-update $REPO
 
       rm "$CFGFILE"
     else
@@ -78,7 +80,7 @@ case "X$1" in
       cat_repo > "$CFGFILE"
 
       # we need to wipe the cache for head.hackage to workaround issues in hackage-security
-      rm -rf "$PKGCACHE/head.hackage/"
+      rm -rf "$PKGCACHE/$REPO/"
 
       echo "http-transport: plain-http" >> "$CFGFILE"
       echo "remote-repo-cache: $PKGCACHE" >> "$CFGFILE"