Open files in binary-write mode in Pull

Fixes google#113 on Windows

Author: fahhem

adb/adb_commands.py

@@ -291,7 +291,7 @@ def Pull(self, device_filename, dest_file=None, timeout_ms=None, progress_callba
         if not dest_file:
             dest_file = io.BytesIO()
         elif isinstance(dest_file, str):
-            dest_file = open(dest_file, 'w')
+            dest_file = open(dest_file, 'wb')
         else:
             raise ValueError("destfile is of unknown type")