Pull nanomsg from our mirror instead of from github.

https://skia.googlesource.com/third_party/nanomsg/

BUG=skia:3027

Review URL: https://codereview.chromium.org/657113004
diff --git a/DEPS b/DEPS
index f883b58..03479b7 100644
--- a/DEPS
+++ b/DEPS
@@ -11,7 +11,7 @@
   "third_party/externals/libjpeg" : "https://chromium.googlesource.com/chromium/deps/libjpeg_turbo.git@82ce8a6d4ebe12a177c0c3597192f2b4f09e81c3",
   "third_party/externals/jsoncpp" : "https://chromium.googlesource.com/external/jsoncpp/jsoncpp.git@1afff032c83e26ddf7f2776e8b43de5ad666c1fa",
   "third_party/externals/libwebp" : "https://chromium.googlesource.com/webm/libwebp.git@3fe91635df8734b23f3c1b9d1f0c4fa8cfaf4e39",
-  "third_party/externals/nanomsg": "git://github.com/nanomsg/nanomsg.git@0.4-beta",
+  "third_party/externals/nanomsg": "https://skia.googlesource.com/third_party/nanomsg.git@0.4-beta",
 }
 
 recursedeps = [