Always write files in binary mode when unzipping

Prevents CRLF conversion on Windows, which was corrupting SKP files
downloaded with fetch-skps

BUG=skia:

GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=4210

Change-Id: Ia876f403d10792ee185d50a29fe30402b733441d
Reviewed-on: https://skia-review.googlesource.com/4210
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
diff --git a/infra/bots/zip_utils.py b/infra/bots/zip_utils.py
index ed1979d..3d25c71 100644
--- a/infra/bots/zip_utils.py
+++ b/infra/bots/zip_utils.py
@@ -55,7 +55,7 @@
       if zi.filename.endswith('/'):
         os.mkdir(dst_path)
       else:
-        with open(dst_path, 'w') as f:
+        with open(dst_path, 'wb') as f:
           f.write(z.read(zi))
       perms = zi.external_attr >> 16L
       os.chmod(dst_path, perms)