Merge pull request #557 from alex/docs-typo

Fixed a typo in the docs
diff --git a/cryptography/hazmat/backends/__init__.py b/cryptography/hazmat/backends/__init__.py
index d1b95f2..41d260a 100644
--- a/cryptography/hazmat/backends/__init__.py
+++ b/cryptography/hazmat/backends/__init__.py
@@ -12,6 +12,7 @@
 # limitations under the License.
 
 from cryptography.hazmat.backends import openssl
+from cryptography.hazmat.backends.multibackend import MultiBackend
 from cryptography.hazmat.bindings.commoncrypto.binding import (
     Binding as CommonCryptoBinding
 )
@@ -23,5 +24,8 @@
     _ALL_BACKENDS.append(commoncrypto.backend)
 
 
+_default_backend = MultiBackend(_ALL_BACKENDS)
+
+
 def default_backend():
-    return openssl.backend
+    return _default_backend