vimproc: Fix when run on non-NixOS linux distros

Prior to this change, if there exists a /lib*/ld-linux*.so.2 on a
system, vimproc will try to load vimproc_linux64.so or
vimproc_linux32.so instead of vimproc_unix.so, which is what nix
actually builds.

pkgs/misc/vim-plugins/default.nix

@@ -647,7 +647,10 @@ rec {
     buildInputs = [ which ];
 
     buildPhase = ''
-      sed -i 's/vimproc_mac\.so/vimproc_unix\.so/' autoload/vimproc.vim
+      substituteInPlace autoload/vimproc.vim \
+        --replace vimproc_mac.so vimproc_unix.so \
+        --replace vimproc_linux64.so vimproc_unix.so \
+        --replace vimproc_linux32.so vimproc_unix.so
       make -f make_unix.mak
     '';
   };