Bump to branch-heads/52

[arlolra]

@keroserene you ok with this? Please give it a spin.

Closes #39

[keroserene]

Gave it a spin, works fine locally on my end! But looks like the OSX travis build is complaining:
==976==ERROR: AddressSanitizer: stack-buffer-overflow on address 0x7fff5fbfefb1 at pc 0x00000573e1bb bp 0x7fff5fbfef10 sp 0x7fff5fbfe6c0
at
#0 0x573e1ba in wrap_memmove (/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/clang/7.0.2/lib/darwin/libclang_rt.asan_osx_dynamic.dylib+0x3a1ba)
Any ideas what might've changed with Xcode/clang at this latest branch head?

[arlolra]

Yeah, I've been able to reproduce that on master as well though. But only on OS X. So, unrelated to these changes.

I filed golang/go#16150 for it.

[arlolra]

Notice it did pass in https://travis-ci.org/keroserene/go-webrtc/builds/139388393, so it seems transient.

[keroserene]

👍