go-1.6: fix the build

One of the test scripts dynamically creates and executes a bash script,
which attempts to use `/usr/bin/env bash`. This patches the file to
use the stdenv's shell instead.

Otherwise, the only way this could have worked was by building go_1_6
outside of the sandbox.

(cherry picked from commit 0547fd247f9960eeffd01973c55ed99112a57205)

pkgs/development/compilers/go/1.6.nix

···
     cd go
     patchShebangs ./ # replace /bin/bash
 
+    # This script produces another script at run time,
+    # and thus it is not corrected by patchShebangs.
+    substituteInPlace misc/cgo/testcarchive/test.bash \
+      --replace '#!/usr/bin/env bash' '#!${stdenv.shell}'
+
     # Disabling the 'os/http/net' tests (they want files not available in
     # chroot builds)
     rm src/net/{listen,parse}_test.go