Valgrind reports allocated mem at close

I ran valgrind on some code I had written and found that some memory isn't deallocated on close. This probably doesn't matter unless you keep closing/opening the X lib a LOT, but it's nice to tidy up after ourselves ;). I used x11_dl, haven't checked x11.

Of course it might be a leak in X, or some mem that can only be allocated once, in which case it doesn't matter.

Valgrind report

```
==4119== Memcheck, a memory error detector
==4119== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al.
==4119== Using Valgrind-3.13.0 and LibVEX; rerun with -h for copyright info
==4119== Command: ./target/debug/main
==4119==
==4119==
==4119== HEAP SUMMARY:
==4119== in use at exit: 32 bytes in 1 blocks
==4119== total heap usage: 136 allocs, 135 frees, 83,124 bytes allocated
==4119==
==4119== 32 bytes in 1 blocks are still reachable in loss record 1 of 1
==4119== at 0x4C2EF35: calloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==4119== by 0x4E3A63B: ??? (in /usr/lib/libdl-2.26.so)
==4119== by 0x4E39F21: dlopen (in /usr/lib/libdl-2.26.so)
==4119== by 0x148E98: x11_dl::link::DynamicLibrary::open (link.rs:90)
==4119== by 0x149391: x11_dl::link::DynamicLibrary::open_multi (link.rs:119)
==4119== by 0x14A6C6: x11_dl::xlib::Xlib::open (link.rs:57)
==4119== by 0x11C1A8: main::run (main.rs:7)
==4119== by 0x11CBB6: main::main (:4)
==4119== by 0x17E6DC: __rust_maybe_catch_panic (lib.rs:99)
==4119== by 0x17811B: try<(),closure> (panicking.rs:459)
==4119== by 0x17811B: catch_unwind (panic.rs:361)
==4119== by 0x17811B: std::rt::lang_start (rt.rs:59)
==4119==
==4119== LEAK SUMMARY:
==4119== definitely lost: 0 bytes in 0 blocks
==4119== indirectly lost: 0 bytes in 0 blocks
==4119== possibly lost: 0 bytes in 0 blocks
==4119== still reachable: 32 bytes in 1 blocks
==4119== suppressed: 0 bytes in 0 blocks
==4119==
==4119== For counts of detected and suppressed errors, rerun with: -v
==4119== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)
```