crystal: fix build in chroot environment

previous build failed on hydra because /usr/bin/env
do not exist in a chroot build environment.

pkgs/development/compilers/crystal/default.nix

@@ -57,6 +57,9 @@ stdenv.mkDerivation rec {
   '';
 
   buildPhase = ''
+    # patch the script which launches the prebuilt compiler
+    substituteInPlace $(pwd)/crystal-${version}-1/bin/crystal --replace \
+      "/usr/bin/env bash" "${stdenv.shell}"
     ${fixPrebuiltBinary}
 
     cd crystal-${version}