data/fonts: simpler cleanups

pkgs/data/fonts/tipa/default.nix

@@ -2,7 +2,7 @@
 
 stdenv.mkDerivation {
   name = "tipa-1.3";
-  
+
   src = fetchurl {
     url = "mirror://debian/pool/main/t/tipa/tipa_1.3.orig.tar.gz";
     sha256 = "1q1sisxdcd2zd9b7mnagr2mxf9v3n1r4s5892zx5ly4r0niyya9m";
@@ -13,9 +13,13 @@ stdenv.mkDerivation {
     mkdir -p "$PREFIX" "$out/share"
     make install PREFIX="$PREFIX"
 
-    ln -s $out/texmf* $out/share/
+    ln -s -r $out/texmf* $out/share/
   '';
 
+  outputHashAlgo = "sha256";
+  outputHashMode = "recursive";
+  outputHash = "1g2cclykr6ax584rlcri8w2h385n624sgfx2fm45r0cwkg1p77h2";
+
   meta = {
     description = "Phonetic font for TeX";
     platforms = stdenv.lib.platforms.unix;